One mild irritant with AudioScrobbler is that you can't seem to get your listening history data out in any reasonable way. This is mitigated by the fact that you could write a custom plugin to record the information in your own local data store, or configure a prebuilt plug-in to go through a proxy that does the archiving.
Hmmm, I wonder if you could build a fully distributed P2P version of AudioScrobbler with easy to manage social boundaries, backed by good security and privacy, nice global statistical services and a well designed query interface?
I can dream can't I!