Most of the bad reviews were written 6 or 7 years ago. I am surprised that Amazon allows these outdated reviews to remain on this site. Not very responsible on the part of Amazon! While the basic design on KitchenAid mixers does not change over time, the construction certainly does.

MODEL NUMBERS: Also notice the specific model number for each review. Since KitchenAid doesn't change the exterior appearance, you will see that many people are reviewing outdated products. The current production of this mixer (as of January 2014) is the KP26M1X the letters after that are color indicators. Most people are NOT reviewing this current model mixer. You would not know that unless you checked the KitchenAid web site. So if you're thinking of purchasing now, look for the KP26M1X, or if you're purchasing later check the web site for the most current model number.

DURABILITY: The mixer now has all metal gears and metal gear box. This unit has not had plastic gears for 5 years. The other common thread I saw in the negative reviews is the owners apparently either did not read the instructions, or thought that as bakers, they knew "better" than the instructions. (1) Never knead dough on a higher speed than "2". With other mixers which have less powerful motors and that old HOOK dough hook, the mixer had to use a higher power to produce the same torque. This mixer utilizes a new style of dough hook and the power of the mixer do a great job on the number 2 speed setting. And (2) do not knead the dough longer than 2 or 3 minutes. I have been making bread and pizza dough for years, and at first I was skeptical about the knead time as well. But after reading some of these reviews about motor overheating, once the dough was thoroughly mixed, I only let it knead for two minutes. It turned out perfect every time. I use mine several times a week and it works perfectly every time.

NOISE: I agree that it makes more noise than my Artsian model which I used for 20 years. The metal gears probably do create more contact noise and the mixer could possibly be sound insulated, but I suspect that would trap heat inside the motor--which you would not want to do. It is not so loud as to be objectionable (not to me at least), but it makes more noise than the Artsian does.

PERFORMANCE: Someone complained that the beater leaves unmixed residue in the bottom of the bowl. Again, read the manual. There is an adjustment point where you can raise or lower the bowl slightly when it is in the "up" position. Mine was fine right from the factory, but some adjustment may be necessary. I make crepe batter frequently, and used to prepare it with a simple whisk. Since this mixer is so heavy, and since I have space to leave it on an island counter now, I started using the mixer to prepare crepe batter. I simply put all the ingredients in the bowl at one time, click on the whisk, and walk away. In a minute or two the batter is perfect - nothing left un-mixed in the bottom of the bowl. Much easier than doing it by hand and the clean up is the same as if I used a metal bowl and a hand whisk. Perfect!

ACCESSORIES: There is a beater that KitchenAid sells separately that I feel should be standard on all their mixers. It includes a silicone "scrapper" attached to one side of the beater blade. It scrapes the bowl as it mixes. This would obviously not work well with heavy batters (like bread), but for mixing thin batters it is ideal. I have ordered this, which you can get from Amazon. Be careful to order the correct size, the KP26M1X series has a 6 Qt. bowl. I know there are other brands that make this beater, but they are within a couple of dollars of the KitchenAid and I know the KitchenAid brand will fit the bowl correctly so why take a chance. Also, aftermarket beaters with the scraper on both sides may create too much drag on the motor.

CONVENIENCE: This mixer uses the lift mechanism rather than the "tilt head" to remove the beaters from the bowl. I do find this to be less convenient than the Artisan and I wondered what the advantage could possibly be. Then I realized that with a 6 quart bowl, the beaters are much larger than the Artisan and would not clear the bowl when attempting to tilt the mixer back. That's the only reason I can see that there is the lever to raise and lower the bowl. It is slightly more inconvenient to change beaters, but once you get used to it, it's hardly noticeable. The pouring shield was a nice addition, as I did not have that with my Artisan and you know what a mess that can be if you're not careful sometimes.

As you can tell, the mixer is very heavy and large. That makes it hard to store, so it's best if you have space to leave it on the counter. I have discovered that since it is on the counter all the time now, I use it for everything. I also have a KitchenAid hand mixer that was once the "go to" mixer, but I haven't even reached for it since this one is always available now. So leaving it on the counter is an unexpected convenience. As I said, I have plenty of counter space; that has not always been the case so it's something you would want to consider.

Another good point is that all the power hub attachments that fit the Artisan will also fit this model. I have the grinder attachment that I have used for years to grind my own beef, so it was good to know I would not have to purchase another.

I feel prospective consumers need to read reviews written on the CURRENT model numbers during the CURRENT production cycle. Why would a review for a model made 14 years ago apply to the model being produced today? Just because the shell looks the same? It doesn't make any sense to me. I do believe that KitchenAid listened to the remarks about earlier models and used those to improve on the current model.

If the mixer does fail to be as durable as my old one, you can bet I'll come back here and let you know and change the review accordingly. But for now, it's everything I hoped it would be.

UPDATE: 1/15/12: Please note that my original review was written in 2007, so serial numbers mentioned are different now, so unsure what has changed at KA. Hope all is good by now!

NEWLY EDITED 11/30/07:
IF YOU ARE ABOUT TO BUY a PRO 600 & you have done your research, you already know there is a plastic/metal parts issue, so PLEASE read my info: KA customer service KNOWS which Pro 600s have the metal transmission cover "fix" (via serial numbers), but some reps are refusing to give you the serial numbers to look for; but they might "allow" you to call them from the store with the serial number off a Pro 600 box before you buy to ensure it has the metal transmission cover. So, be insistent! Here's my story:
The first rep I called was a supervisor "Kelly", who refused to tell me which serial numbers to look for! Nice! I spent too much time researching ,so I called back & the next rep (Rachel) gave me her extension & told me to call her from the store & she would tell me if the one I found was made after the "fix". By the time I found one I wanted - at the second store visited - KA cust serv was closed. I bought it anyway, crossed my fingers, & called the next day. "Rachel" wasn't available, but another rep told me the serial number was one of the newer mixers I wanted. (pls read all the "negative" reviews here for good info)
IMPORTANT: This rep also gave me crucial I want to pass on as it's the info I tried to get before I bought my mixer - the serial numbers of the Pro 600 6 qt, 575 watt mixers with the metal cover "fix" (made from mid-April 2007)begin with numbers higher than "14" (my serial number is WU1503109, so it's above "14") Depending on the rep you get, only a couple are willing to confirm this info, so be prepared for frustration but just hang up and keep trying until you get a good rep.
ALSO IMPT: There are a few 6 quart KA mixers made - I am only speaking of the store bought PRO 600 6 QT, 575 watt mixer found in stores like Bed N Bath/Linens N Things. So, read all these reviews carefully & note the dates they were written - I think there is a possibility of people writing both pro & con reviews about 6 qt mixers that might be different. However, the plastic issue is the same, just the power would be different. For example, QVC sells a 6 qt KA mixer with a smaller motor, and there's a Williams Sonoma 6 qt mixer as well.
I wanted this powerful mixer as I have a 30 yr old KA mixer with a 250 watt motor, but it has a small bowl. My old mixer has never had a problem with a thick batter cookie I make every year at this time. I was anxious for the large bowl & to see how my new "workhorse" with its 575 watts would handle this batter because many have complained that it burns out on thick doughs/batters. UPDATE: I just made my thick cookie batter with my new 575 mixer & it did a super job!( My recipe uses 1 1/2 lbs of brown sugar, 8+ cups of flour, one pound of butter and 2 cups of Karo syrup - no other liquids or eggs so it's a tough batter for any machine) Once I began to add the flour (using the nice pouring shield) I never went above speed 2 (as suggested by KA for heavy batters/doughs) & speed 2 was all that was needed. A nice rep also suggested to rest the mixer if I needed to mix beyond 7 mins, but I never came close to that.
SIDE NOTE: when I opened the box last nite, the electric cord was folded in half & tied into a knot; there was a very sharp/jagged piece of metal on the lifting guide; a blob of dried paint on the top of the bowl holder; & bits of white crystals in the bowl that tasted like salt. Of course I called KA & Robert, with permission from his supervisor, offered a replacement immediately which I didn't ask for & certainly wasn't expecting! He said the "presentation upon opening the box" wasn't professional & they wanted to correct that. He also told me to go ahead & use this unit until the replacement arrives! WOW! Once it arrives, KA will send UPS to pick up the one I bought. Another WOW! I then told Robert about my Serial Number fiasco & he said that he would have provided the S/N info before I shopped! He also said that he stood by his fellow reps, but he agreed that someone like me, who had done hours of research, should have been given the requested info from the first call & certainly not have been forced to call from a store! In my case, I wanted a mixer made after the mid-April date which is the date KA began putting metal transmission covers on instead of plastic.
My WARNING: There is old stock, with the plastic cover, out there, yet KA still insists there is nothing wrong with this, so I'm giving you a big head's up..
Until I made my batter, I rated this mixer a 2 for the lousy customer service/runaround I got from 2 of 5 reps. Now that I've made my batter, I am vamping it up to 5 stars BUT KA needs to get more reps like Robert and the other guy who helped me. (If not for them, KA would NOT have this sale) So, while I wasn't treated right at the beginning, I am happy now & have edited my review accordingly. KA has quality issues re cust serv, especially supervisor "Kelly". (Try to avoid her as she thinks she works for the CIA.) I hope I have saved at least ONE person from all the frustration I suffered through to get what I wanted. In the long run, I think you'll be happy & customer service is great IF you get a good rep!