Article:
http://www.forbes.com/2007/05/16/cheap-pc-...516cheappc.html
Slideshow:
http://www.forbes.com/2007/05/16/cheap-pc-...thisSpeed=30000
Digg discussion:
http://www.digg.com/hardware/The_cheapest_...World_right_now

I guess they'd be pretty good for someone that doesn't do anything demanding with their computer... or good as a spare computer. If you only have one computer and someone else is always using it, then this is great. Or if something is wrong with your main computer, then you have a backup. Maybe you just want to put another computer in a different room? :eyepop:
Or maybe if you just don't want to spend extra money on a full-power state-of-the-art computer. But they're no good for demanding tasks.... so don't expect to edit videos well or play Farcry on one.