Anyone finding problems with their iTunes Genius?

Anyone else finding that their iTunes Genius function only works at the moment they buy a new track? Mine doesn't work at all on previously purchased tracks. I've contacted Apple and they say it works fine. I kinda smell a scam. Is it just my Mac maybe? Failing this, who wants to play Genius and suggest bands on the following lines: Seabound, Front 242, Killing Joke, Frontline embly, Covenant, Diskonnected, Project Pitchfork, Diorama et al