I been looking for this solution for over 4-5 months for a torrent box aka 24x7 pc & a music file server (or something to stream mp3 off it)
I considered min-itx pcs, thin clients, old broken laptops, NSLU, ADSL Router + Torrent type things.. & even mac-mini
We have around 6-10 hour of power cuts here in NCR/Delhi everyday (Yea its a village

). Even with powerbackup/inverters and stuff, my power hungry pc does not last for more than 2 hrs. & so my search for a reliable 24x7 box started.
Pricey Apple FanBoy Option: So I was kinda tilting towards macmini (although I wouldnt buy it anytime soon, I think it awaits an upgrade) coz i believed it wud be reliable than other miniitx pcs, its got wifi which was big plus point a beautiful eye candy os which can replace my main PC. I think it would take say 30-60W when downloading (I didnt want the pain/fun of assembling all the mini-itx components) but hey its Apple, its expenisve.
Cheap Laptop Option: So my second choice was EeePC, and plugging in the 16G USB thumb drive to it or those portable drives. Very low on power, has wifi & everything but a low disk space (I just hate that tiny resolution, good thing is it can do 1280 x 1024 via external monitor)
Cheap MinITX Option: Another choice was the Koolu.com thin client, I can add my own drive & maybe upgrade the RAM & it will be able to stream music if needed, but wait it doesnt do wifi, maybe usb-wifi would do it good. And hey its geode processor low on power.
My current setup:
I am using dell insp 1720 as 24 hr download lappie. Its connects to my Airtel wifi connection most of the time, but at nights 2.20 AM it connects to BSNL ;-) & starts sucking the tube.