Asus Zenbook Primes seem to be a very high quality Ultrabook series as well (be wary of the differences between 32VD/32A and 31 models)
Also, the Zenbook Primes mostly have 1920x1080 resolutions. While the X1 Carbon was upgraded from a pitiful 1366x768 to a 1600x900 resolution, it's a shame they are still a bit backwards on that. I'm wondering what people think on the 1600x900 vs. 1920x1080 issue and how much of a difference it makes.
I don't have a true Ultrabook but I do have a Sony Vaio Z with a 13.3" 1920x1080 screen in it. I run it full resolution in Windows 7, with everything scaled down to standard size. Is everything very small? Yes. But when I'm sitting in front of it it's not much different than being a couple feet from a monitor and it truly gives me usable space. It's my travel machine as I am on the road a lot, and since I've had it coding in a hotel room is finally productive for me.
My understanding is that the thickness comes from the fact that the body isn't a single piece of metal, so you can swap out the RAM and HDD (unlike the 31A and 21A). Also, apparently you can repartition the SSD that's used as an OS cache into a separate drive reasonably easily.
As much as I'd prefer the formfactor of the 21A, the ability to upgrade to 8GB of RAM is too big of a selling point to pass up on the 32VD.
The 32VD is bigger/thicker than the 31 models and has a hybrid HD(24GB flash) rather than full SSD. It's got a dedicated graphics so I guess it's just targeted towards a different market.
Also, the Zenbook Primes mostly have 1920x1080 resolutions. While the X1 Carbon was upgraded from a pitiful 1366x768 to a 1600x900 resolution, it's a shame they are still a bit backwards on that. I'm wondering what people think on the 1600x900 vs. 1920x1080 issue and how much of a difference it makes.