No need to buy from iTunes. You can "like"any album or song in itunes store. Just search for what you want and there's a little dropdown menu that will let you like or share it on your profile.

yea but i want it to be automatic based on my listening habits... like last.fm ;)

Gotcha. I like that idea too. I think apple will be improving it over time. But they should have put in more features like that and others off the bat.

Well, it's all about driving sales activity to the iTunes store, but I really don't get why they haven't thought to lift playcounts from the library or hook it up to last.fm.