Didn’t really get the idea of social networking your music, and still not too sure, but I’ve signed up for last.fm and found that Rockbox* and Slimserver both support updating your last.fm profile with what music you’ve been listening too (this is known as ‘Scrobbling’).
So I can have my music profile updated now when using my iRiver (through Rockbox) and Squeezebox (via Slimserver).
Why anyone would be interested in my music profile I don’t know, but here it is: http://www.last.fm/user/tj_moore/
What’s useful though is to see for myself what my tastes are like, and to some extent it’s handy to remember what I played recently (I tend to go through album by album for a particular artist so I like to continue where I left off).
last.fm actually has it’s own software which acts as music player, but you don’t have to use it to ‘scrobble’. It does allow you to listen to their own radio station though (but apparently there is a plugin for Slimserver to do this also).
* – Rockbox is open source firmware for mp3 players, offering better file format support (no DRM support though… but that’s a good thing), rich features, gapless playback on devices that don’t support it, even videos on devices that never played videos!, and games (e.g. Doom).