i bought a used 701 for 180$ and just bought a 2GB RAM upgrade / 16GB SD for ~99$ total.
all i need is a web browser and a terminal (for ssh/screen/irssi purposes), so it works really well for me - I'm a sysadmin.
if you like futzing with Linux it kicks ass. there's a solid Eee community out there and are docs all over on how to do everything. the keyboard takes some getting used to, but I don't mind it. i still need to remap the shift key since they crammed the up arrow in where shift should be. no biggie.
don't go with the stock Linux distro (Xandros) it comes with. I tried the Ubuntu release for Eee but Debian Lenny kicks the crap out of it. the Ubuntu release was just too buggy for me (compiz causes issues with the default media player).
it's kinda pricey brand new mind you. it's a total novelty if you can get it @ the right price.