I picked up a Dell mini-9 about a month ago. They had a special running, so I got myself one with Ubuntu, 1GB RAM and 8GB SSD; one for the wife with XP, 1GB RAM, and 16GB SSD. Came to a little over $600 for both, after tax and shipping. So far, we love them. In fact, I was so impressed with the Ubuntu Linux distro I've gone and redone my webserver with Linux after 8 years on Windows Server.

I occasionally throw this in the bag with my 15.4" work laptop, since it gives me more flexibility. The total lack of moving parts (and noise) is very nice...