I am running mt-daapd on a NSLU2 with Debian/Etch without any problems serving my computers with music. Only standard Debian, no own compiled software. I ony have around 2000 songs though.
The slug clock in with 266MHz and 32 MB RAM. No performance problems, except on thing. I have all my songs (nearly) coded in OGG, and the default installation try to convert all those to MP3 when delivering. THAT is something the SLUG can’t do. But after removing all media converting in mt-daapd on the SLUG, it works great. That is not a problem, since all my clients can handle OGG-files.
My SLUG and disk (an external 250G USB-disk) use about 5-10 W. Which no PC I know about can match. So it runs all day long (working also as file-, web-, NTP- and soon printer-server at the same time).