I just found AudioScrobbler, the idea sounds nice though I didn't get to find any musical neighbours yet.
The XMMS plugin is just crap! It hangs when there is an ID3v2 tag, I fixed that and provided the patch to the Debian BTS. The author should learn about reusing libraries and find some that implement this code already. Or at least copy code from another GPLed app instead of inventing his own.