If you haven't already seen it, Musicmobs is a great online music community and music suggestion engine, among other things. It works best with iTunes, especially if you use a Mac--in which case you can also use the cool Mobster software that integrates seamlessly with iTunes--but it's also great for Linux users as well if you use Rhythmbox, an integrated music management system inspired by iTunes.

Musicmobs is simple to use: Just sign up (you don't even need to fill out a big form to do so) and upload your iTunes XML library file. Then Musicmobs lets you see what music you have in common with other users, gives you music suggestions, and links songs and albums to the iTunes Music Store (one feature you can't get in Linux of course). It's fun to browse through the artists and the various Musicmobs user pages to see what others have. You can leave comments on their pages or add them to your list of favorite users as well. I like Musicmobs because, unlike most "network" web sites, Musicmobs is very focused on one thing: music. It's not a dating service or a way to set up parties or anything like that.

To use Rhythmbox with Musicmobs, I have a crude Perl script available here that you can download and run rather easily to parse your Rhythmbox XML library file and upload it to Musicmobs.