One thing I would love to have in my MonoLoco music app is a feature mentioned at the top of Aaron's interview "what bands that my friends like are playing around here in the next week?". The idea would be that the app knows your friend because you IM program and email program have been creating a certialized FOAF file for you (hey maybe your phone is bluetoothing info about who you talk to the most as well), so you can collect who you talk to a lot (at least via computer). Hopefull you talk to your friends a lot and don't spend all your time flaming people. Then MonoLoco knows who you and your "friends" listen to (maybe you want to know what the people you flame listen to as well), using MusicBrainz identifiers to catalog it. It should also use a yet to be written feature of Musicbrainz to find the bands homepage, and then MonoLoco will autodiscover their RSS feed with news (which monoloco will display on screen while you play that bands songs), and another for tour info. If the tour feed is done will it will have links right to where you can buy a ticket.
The UI for deciding who to share your MonoLoco info with would idealy piggyback your IM client.