Slashdot has a discussion on new VIA low power technology. I bought a Chinese PC for $199 about a year ago that uses VIA chips. This PC runs on very little power, and the single fan is small and quiet. I bought it to use as a web server.
For most computer users, I question how much processing speed is really required. Because I am now using an old Mac G4 tower (with OS X) for running my Java based web demos my Chinese PC has just been a spare computer until recently when my wife grabbed it - she likes how quiet and cool running (important when you live in Arizona!) it is. At least for $199, if I need another Linux box, I can buy a replacement instead of "negotiating" to get it back.
Anyway, even when developing Java code using IntelliJ or Eclipse, a 800 MHz $199 Chinese Linux based PC is fine. (I am using dual G4 Mac for development, because someone gave it to me as a gift - but I would trade some of that processing power for less noise and much less power consumption).