Some time ago Anders created a last.fm group for YayArt. Anders showed me how Rhythmbox can integrate with last.fm, reporting in what I'm listening to. So I ended up creating a profile.
At first I find last.fm pretty confusing and leave it at that. A couple of days pass where I play music from my personal collection with Rhythmbox. Then I visit last.fm again. Behold, now it has lots of interesting suggestions. I just click "Play your recommendations" and I get a pretty varied assortment of music. You can control the stream to some degree by either hitting love or ban to what you're listening to.
There are some minor glitches, e.g. I yesterday loved too many film music pieces so it was getting a bit stuck on that kind of music until I started banning some of the pieces, but overall it's working incredibly well.
An interesting side effect is that you can listen to people's music taste. Now if I only knew someone on last.fm whose music taste I would like to listen to... My profile is here in case you want to listen to mine.