Truth be had, I've been pretty disappointed with ultrabook offerings so far - low resolution screens, terrible keyboards and below average power. With the UX31A and UX32VD series, Asus promised to change all of that, and, in my opinion, succeeded remarkably well.
1. Design/Aesthetics. This is a very pretty machine. It's lightweight, looks good and doesn't seem to smudge. Not much more that I can say here - it's pretty and sleek. I wish that it had a MacSafe power adapter instead of the right angled plug, but I guess we have patents to blame for that.
2. Keyboard. The keyboard on this machine is fantastic. I would put it in the same league as the MacBook Air's keyboard, which is to say that it is very very good. In comparison, I thought that the keyboard on the original Zenbook was terrible. It's not quite as nice as the keyboard on my Lenovo T430, but it is still really high quality, and probably the best ultrabook keyboard currently available (and backlit, too). Love it. Some people have mentioned keyboard flex - there is a tiny bit if you push down hard near the middle of the keyboard, but it's not something that I would have noticed if I wasn't looking for it.
3. Screen. The screen is excellent - beautiful colors, 1080p resolution. There was a bit of backlight bleeding, but it's only in a few places, and it's only noticeable if the screen is entirely black, so really not a big issue. When the screen is not purely black, you couldn't even find it if you were looking for it. By default, the display is running at 40Hz - not sure who was responsible for that decision - which made things look choppy. Setting it to 60Hz fixed that problem though.
4. Software. Includes standard PC bloatware, which is kind of annoying but it is easy enough to remove. Of particular note is the Asus Update Manager, which is supposed to pull updates from Asus' website, but in reality just crashes repeatedly (I booted my Zenbook the first time to Asus's update manager giving me a wonderful stack trace as it died). Other included software is of similar low quality - I'd recommend wiping the machine when you get it if you can. Also includes software for a touchscreen/pen - I'm not sure what that's about, since this machine has neither.
5. Touchpad. I hate touchpads. This one seems responsive and sleek, but I just switched to using a mouse and disabled it. YMMV. Edit: Played with the touchpad for a bit, and I have to admit, I kind of like it. It's not as usable (in my most humble opinion) as the nub on a Thinkpad, but it gets the job done. Some settings I found to make it nicer: Turn off tap to click, so that your mouse doesn't click randomly while you're typing. And turn off Inertial Scroll in the Elan -> Multi-Finger -> Scrolling setting. It's makes scrolling choppy for some reason. Unfortunately, multi-touch isn't as integrated into the operating system as it is with OS X, so I feel like we'll have to wait until Windows 8 to see the true power of this touchpad. In its current form, the touchpad works as advertised - it's responsive, smooth and very configurable.
6. Graphics. This machine has a dedicated graphics card, and while it's not the most beefy, it's certainly an improvement over the standard Intel 4000. Linux users note: This uses nVidia Optimus to switch between the integrated and dedicated graphics cards, which apparently doesn't have very good Linux support yet - so if you plan on running Linux on this, do some research first.
7. HDD. 500GB HDD. In 2012. Unacceptable. However...
8. Upgrades. This is why I bought this machine. You can put an extra 8GB of RAM in (in exchange for 2GB of the built in 4GB) for a total of 10GB of RAM. You can also swap out the HDD for an SSD, which is awesome - get one with a 7mm height though, or it won't fit.
Overall: If you are willing to upgrade the HDD and RAM, get this machine - you won't regret it. It's light, it has a beautiful screen, an excellent keyboard, it's very fast, and with the upgrades, it is the nicest laptop that I have ever owned. If you are not willing to upgrade, I would say that you should get a MacBook Air or the Zenbook UX31A (or the Sony Series Z if you are willing to spend more) instead - the SSD makes a huge performance improvement. I give it 4/5, because you have to spend a bit of time to clean up the garbage on it and install a better hard drive and more RAM, but once you do that, it is unmatched. Also, Microsoft is apparently going to offer a $15 upgrade to Windows 8 Professional, which is a great deal.
EDIT:
After a week with this machine, some more thoughts:
Really liking the trackpad. Turning off tap to click is key - it is downright bizarre that the default has those settings on, I think that every reviewer complaint about the erratic touchpad is due to this setting being on. After turning it off, it's smooth, accurate and actually really nice to use. I upgraded to the Windows 8 Release Preview, and for a while I was wondering what the heck was going on when things were randomly being clicked and dragged around, before I realized that I had to disable tap to click again.
As for the keyboard - after working with it for a while now, I don't like it as much as the MacBook Air's. It's still a very good keyboard, but the keys are a bit flimsy feeling for my liking, and - very occasionally - a keypress gets missed. Not bad by any means, but it could have been better. If you are really looking for a great typing experience on an ultrabook, you may want to wait to check out the Lenovo X1 Carbon, which should be available in August. Again though, the keyboard is very usable - I'd put it as better than the Samsung Series 9, but worse than the MacBook Air - and both of those machines have very nice keyboards. On the upside, keyboard flex on the UX32VD is definitely a non-issue.
Also, Asus's included software is bizarrely bad. Don't even try to use it. It doesn't work, or it crashes, or it uses a ton of CPU, or it just looks plain ugly.
Finally, if you are planning on upgrading the RAM, see the comments on this review - I installed an 8GB 1600MHz stick, but it is only running at 1333MHz for some reason. This apparently has to do with the CAS latency of the onboard stick vs. the new one. I don't know how to get around this, that said, I wouldn't have noticed the difference if I didn't check the settings.
Still, very happy with it. I haven't put the battery through its paces, but unscientifically, it seems to last about 4 hours under high workload (writing code).
Anyway, knowing what I know now about this machine, I would be less hesitant to buy it than I initially was. It is very much an awesome computer.
EDIT (3/5/2013):
Months later, after using this extensively, taking a star off. This laptop has since become my primary machine, and I use it for hours every day. Since I wrote the review, I've upgraded to Windows 8 which I actually find really nice. (As an aside - and this is NOT reflected in my rating - I found Linux (Ubuntu distro) support somewhat depressing. Some keyboard Fn shortcuts didn't work - in particular, brightness display - the battery life was under 2 hours, and sleep didn't work at all. YMMV, though - I run a VM now for my Linuxing).
Mostly I use this machine for writing code and basic internet stuff.
The machine is still speedy, and the screen is still beautiful - Asus deserves a ton of praise for that. Battery life is about what I thought it was - 4 hours on average under my normal usage, which isn't anything to write home about these days, but it's certainly more than adequate. I can even play modern games - usually I have to lower the graphics, but on medium settings and at 1600x900, most games run at a smooth 60fps, which is impressive.
Things that I don't like though are the little things. The keyboard isn't as great as I thought it was - I find that I miss keys, even when I clearly pressed them down. Again, it's not terrible, but Lenovo and Apple both do much better, and for a $1500 laptop I expect a lot. My hypothesis is that the keys click (both physically and audibly) slightly before the button press is registered, and as a soft touch typist, it causes me to release the key milliseconds too soon.
The touchpad is pretty bad too. The hardware itself is fine - it's accurate and spacious, but palm rejection is just too bad to be useable. So I use a wireless mouse instead.
And the software - oh the software. The wifi driver crashes every day or two, so I have to restart my laptop frequently. And when I put it to sleep by closing the lid, sometimes it doesn't go to sleep, so when I pull it out of my backpack it's too hot to hold and the battery is almost dead.
So overall, this is not a bad machine - it has some very excellent points, in particular the display - but my problem with it is that it's not the premium experience that I would get if I'd bought an Apple computer for the same price. The keyboard is mediocre, it doesn't always go to sleep, the built in software crashes, and the touchpad is unusable. And while I can deal with all of these things, I feel like I shouldn't have to, considering that I paid top dollar for this (and then some to upgrade it).
The end result is this: I'm going to buy a new laptop, probably this summer when Intel releases their new line of chips (Haswell). If Lenovo brings out a laptop with a nice screen (for example, an X1 Carbon with a 1080p display, or the Yoga 11S with at least 1600x900), it'll be a Lenovo, since their keyboards are unmatched. Otherwise, I'm going to switch to the evil empire and get a Mac.