I think it sounds like a great idea. There are a lot of songs out there that I would like to listen to, but not necessarily own. Too bad they took too long to jump on the music store bandwagon.
allofmp3 works very well though...about what I'd like ITMS to be. I get to chose almost any bitrate, any file type. I was curious so i bought a GB on there for $10, been downloading songs all night...its pretty sweet