I bought a Toshiba Z830 ultrabook for software development. I was unsure at the beginning if the thing would be fast enough, but very satisfied with my purchase after 3 months using the Z830 every day for development.
The Z830 implements Intel's ultrabook spec. It has an Intel i5 1.6GHz processor, 13.3 inch LCD, and weighs 2.5 lbs. It's got 6Gb RAM and a solid state hard drive. Build quality is what you'd expect for a laptop; adequately strong but certainly not bulletproof. There's one very scratchy point on the metal case where that tiny lever on the RJ-45 network connector snaps in. Plenty of interface connectors, but I still had to buy a USB hub.
I generally use my Z830 on a desktop, connected to a 21 inch monitor and full-sized keyboard, but I also use it "on the road" with its own display and keyboard.
I am a full-time software developer. I'm currently using Microsoft Visual Studio 2010 to compile C++ jobs. I was a bit concerned about what kind of performance hit I'd take buying an ultrabook, but I've got to say, the Z830 is a screamer. I suspect a lot of the performance comes down to the solid-state drive. In the 21st century, compiles are I/O-limited. I'm sure you can own a machine that is faster, but can you carry it around? Most of the time I don't run the Z830 hard enough to spin up its tiny fan. (The fan isn't annoying even when it spins up. I hate fans).
I do carry my machine around. It commutes to work and back with me, where I use it for a little web surfing. No cell modem; I load up a batch of web pages before I leave, and read them on the bus. It goes to meetings to take notes.
For many years, it's been my intuition that one kilogram was the magical weight at which you could carry your computer with you everywhere, and the Z830 confirms this intuition. It's so small and light that it doesn't weigh down my briefcase; quite the contrary. I had to buy a smaller, lighter briefcase to take full advantage of the light weight of the Z830 (ThinkGeek's tactical briefcase is very geek-chick, and very light).
The keyboard has flat tops. It's pretty hard to keep your fingers on the home keys for typing while jostling around in a bus. The resolution of the built-in LCD is only barely big enough for coding. I wind up closing everything in MSVC 2010 but the edit window. If your eyesignt is keen, you may be able to set a smaller font and do better, but I don't have this luxury.
The battery holds enough charge for half a day's coding. Not enough to make you completely portable, but then, I'm working at a desk so it's no big deal.
The Z830 is light enough to create some new problems; trip on the power cord, and you're gonna yank that sucker right off the table. I did that the first hour I owned it, and bent the pin on the power adapter big-time. Fortunately, new power adapters are inexpensive (like $20) so now I have two. I found that shaving just a bit of plastic off the end of the power connector caused my bent power adapter to seat more firmly.
It's kinda creepy to carry a thousand dollar item around with you. I'm paranoid that I might leave it someplace stupid, and it's so light that it would be easy to do. The rest of the world might be used to losing $600 iPhones, but I am not.
I've been schlepping laptops around for many years. My first laptop weighed 18 lbs. This is the first laptop I am happy to take everywhere. I'm never going back to a regular-sized laptop.