I can't say I quite understand the ultraportable thing (why not just use a real computer?), but I have to admit that the Eee PC from Asus is a slick little device. Not as slick as the Macbook Air, but not nearly as pricey, so still pretty slick. And now it's even slicker- Dan from UltraMobileGeek has figured out how to install World of Warcraft on an Eee 701.
You can see in the video above that it's just barely playable-- you couldn't raid Black Temple (or even Karazhan, I'm sure), but for logging in and grinding or checking mail, it would probably work just fine. The process, unfortunately, isn't exactly simple-- you have to run modified drivers, overclock the PC, and run experimental code (plus, memory might be a problem, as you need an 8gb SDHC card and probably more RAM than you've got now)-- but if you're interested in pushing your Eee to the limit, it might be for you. One suggestion or Dan (and anyone else messing around with this): would the Wine version of WoW let you skip installing XP, since the Eee is Linux-based? Just wondering.
At any rate, sounds like a fun Saturday afternoon project if you've got an Eee to play around with and want your WoW ultraportable.