A few months ago I told you guy about the Buddy Tunes plugin for AIM. This basically made people's iTunes libraries appear like they are on your local network - thereby enabling users to stream music from any of their friends' machines. Since then, Simplify Media has essentially launched a productized version of this (albeit not integrated into AIM). The other approach that was being worked on at AOL before I left is now public in the AIM 6.5 release. It is called "AIM Tunes" and it is a similar concept but ditches the deep iTunes integration for a more player-agnostic approach.
Basically, everyone on your Buddy List (that has the plug-in installed) appears on your AIM Tunes dashboard (in your browser). From there, you can browse their libraries and either stream them directly from your buddy's machines via an embedded flash player - or if you want - to "pop them out" and have your default media player handle them.
You can also create a playlist of songs from all across your network - although it is currently only a single/temporary playlist.
All-in-all, it is pretty slick. It still could benefit from deeper integration into the AIM client (see who is listening to my stuff and better facilitate communication about what's being shared), Mac support, an aggregated "buddy library" view (lets me search seamlessly across my entire network), multiple playlist support, publishing, etc. But, if you use AIM I recommend giving it a whirl. I may end up just running on a separate AIM instance on my home machine (under a separate screen name) and use it to stream to myself. Then again, there are a ton of other options there... Winamp Remote (also an AOL offering), Streampad (although Dan now works for AOL too), and many others.
I'd be interested to know what you guys think of it.