Oh, for those considering going for the registered version, jump in!
The new power search features, moods, etc are really cool.
Basically, you can create a playlist that you really like, save it as binary mood, and send it to a friend. Even if he doesn't have the same songs, this binary mood will select similar ones from his library.
You can generate as many playlist from your library as you want using your mood settings.
There are many more features, but it seems that musicIP is one of the most under-documented applications out there. No wiki, no comprehensive help (just pages scattered over the site talking about different topics), some blog posts, and that's it.
Maybe we need to create a wiki?