I use a Thin Client (Score 1)

I got me one of these http://unixwars.com/2009/02/19/fattening-up-a-thin-client/ for under 75$. I just added an internal HDD for downloads. It has plenty of power and uses standard x86 code, so no problem with the upgrades. It draws from 18 to 27W. Not as little as the ARM alternative, though. It is also fanless, and has a printer and 3 USB HDDs attached through USB, Gigabit Ethernet and has a PCI slot in case you need eSata or whatever. I've been very happy with it so far.