This is a very high quality unit, nicely designed. I chose it over the Honda Eu2000i because it has a fuel gage and is a hair lighter (2 pounds), and liked the styling better. Specs are so close it's a tie... the Yamaha unit specs a bit quieter in "eco" throttle but the Honda specs a bit quieter at full power. Prior to this purchase I had bought a Honeywell inverter generator (a much less expensive Chinese-made knock-off) from Costco which I returned, because I was unimpressed with the Honeywell unit's quality and noise level. While the price difference is major, you get what you pay for in this case. Anyone looking at the cheaper knock-offs should really consider that a 5db increase in noise level is a major difference, the way humans perceive it.
The most impressive thing about this unit is how quiet it is. Even at full engine speed you can stand about 6 feet away and have a normal conversation without raising your voice, or talk on a cell phone without undue distraction. It features an "eco" setting which tapers down the engine throttle and noise when full load isn't required. At half-throttle or less, from about 6 feet away it is about half as loud and amazingly quiet. I used it to run a 50-amp 12v battery charger and at full charge level the charger only required the generator to operate at about half-speed, and when the charger tapered down the charge level to under 30-amps the generator became so quiet I literally forgot about it. It is MUCH quieter than my boat's inboard diesel engine, and more efficient than running the main engine just to top off the batteries. I also used it to power a heavy duty 120v grinder and it had no problems supplying the needed power, even on electric motor start-up.
I got this mainly for charging our boat's batteries at anchor but I also wanted the ability to run power tools. The lighter 1000-watt inverter generators could easily handle the charging application but not the more power-hungry tools. Having the extra power also means the eco-throttle will likely kick in earlier and the unit will operate quieter. The number-1 purchase criteria was "quiet" because I don't want to be distracted by incessant noise or be a bad neighbor in anchorages. The Honeywell was not quiet enough in my opinion.
If generators are abused it will lead to regulations banning them, so an appeal to other boaters and to campers: Please don't settle for "cheap". Get a better quality inverter-generator unit that's quieter so you minimize noise pollution in get-away places. (Leave your "contractors generator" at home!!!) Also, please be considerate of neighbors and limit running it to times/places you aren't as likely to disturb others... and don't leave your boat or campsite while it runs and runs. We all like our electric conveniences, but if you really need 120v power more or less constantly you should either stay home or get a dock/parking space where you can plug into "the grid". It's rude to disturb others who are trying to get away to find some peace and quiet.
Negative: The unit ships without engine oil, so you need to buy a quart of standard 4-stroke engine oil and fill it. You will also need a funnel, and a pan to catch excess oil. There is no dipstick; you need to fill to the level of the bottom of the filler hole until any more runs out. It uses less than 3/4 quart. I think they should have included the required amount of oil, and a plastic filler container with a spout, marked to show the proper amount of oil to use.
Update 7/21/2015: Still running well. I switched to TruFuel and it starts first or second pull even after it's been sitting for months. The generator doesn't use much so the cost is worth it for reliability. Just say "No" to ethanol (and fuel related problems).
Update 10/11/2014: I had my first problem with this unit. It stopped running while in use, after about 30 minutes under medium load. I assumed the problem was bad gas or phase separation, and went through changing the gas and cleaning the fuel system, changed the spark plug (had never changed it in 5 years since new) and checked the oil level. Finally took it into a repair shop and they diagnosed a faulty spark coil. I'm not surprised that an electrical issue developed as this unit is used every summer on a boat in a hostile humid saltwater environment, and actually sat in a few inches of saltwater once. However the spark control circuit (spark coil) is a sealed unit potted in epoxy. I would expect any failure to occur at components or connections that are exposed to air. Perhaps the problem was really at the spark coil connection wire and not within the sealed module itself? Will never know, I paid the bill and it's purring like a kitten again.
Also, a note about tri-fuel conversion: Even though I have had no fuel problem with this unit, I've had fuel issues with outboard and snowthrower engines. I'm still drawn to the idea of doing a tri-fuel conversion for engines that aren't used frequently... But they charge around $200 for the kit plus I'd need to spend around $175 on top of that for a fiberglass tank/hose/quick-connect. A tri-fuel conversion also adds expense and bulky extensions to a unit that is otherwise very sleek, compact and portable. I've decided to use Tru-Fuel instead, on my small engines. It's expensive compared with gas from the pump plus fuel stabilizer, but you can buy a lot of it for the cost of a propane conversion kit, and it might help avoid aggravating downtime and costly repairs. When you need a generator -- you need it to run! Tri-fuel conversion still makes more else if you need extended run-time and portability is secondary.
Update 2/3/2014: I was researching the idea of adding tri-fuel conversion and came across this video on YouTube. Here is the link to the video[...]. I learned in that video (at 1:53 into the video) that the Honda 2000 controls don't allow a user to run the carb dry before shutting down the motor (but the Yamaha does). I think that's a huge PLUS in favor of the Yamaha. I always run the carb dry in my small engines when I might be leaving them sit for more than a few days, to avoid gum formation in the carb. For extended storage I also use the drain screw at the bottom of the float bowl.
Update 2/22/2012: In general still very happy with the unit, but checking oil level is inconvenient (you need to open the case with several screws) and changing the oil is a messy operation involving rags and clean-up because there is no neat way to capture the waste oil or overflow directly into a container. I think the next generation of this product should improve on that design issue and provide a dip stick or oil level indicator that's either externally accessible or located behind a quick-access panel. (Edit 8/21/15 Bill Esposito wrote down below in the comments that he "purchased a pair of these on 8/14/15 and they now come with a door for oil access....no more screws." Nice! Decided to copy that here in the main body of this review so it's more visible to readers.)
Update 8/29/11: Having owned this for almost 2 years now I would add the following: 1) I have found that it has enough power to run the charger AND the hot water heater's 120v heating element at the same time. It is near-max (running full speed) but doesn't light the overload light when doing that and the charger is in bulk phase. Nice when you're in an anchorage for a few days and haven't run the engine. Why run a 57hp diesel just to heat water and charge the house bank?
2) If I shut off the fuel and let the carburetor run dry before putting it away, it does not smell of gas with the fuel vent and fuel valve both closed. The maker advocates storing in a well ventilated area or garage, but odor from fumes is not a problem.
3) It's also useful at home during power outages. I have a larger much louder 5500w contractors generator that plugs into a 12-circuit transfer switch wired by an electrician, but as a courtesy to neighbors I shut that off overnight. I can use this Yamaha unit with an extension cord to keep just the refrigerator running overnight and it stays in 'eco mode' so it practically purrs. Also the fuel burn rate is extremely low so it uses a fraction of what the larger generator would use.