I'm ecstatic to see Apple launch its music service. It may be too early to say, but from looking at the apple site (can't get onto the service right now -- too busy) the service appears to comply with almost every request I laid out last year in a music article. Ideally, it'd be nice if the songs were 50 cents each, but a buck isn't bad, and I can't wait to enjoy the convenience of hearing about a new artist or album, going onto the service, and having my own copies of the songs in a few minutes for a reasonable price (even if CDs will cost as much as physical media, which they clearly should not).
Kudos apple for sticking your neck out and getting the ball rolling on changing a dying industry.
update: Crap, it uses a DRM-loaded AAC format instead of mp3 so I can't share it with my PC player. Even though winamp does read AAC files, it appears that both version 2 and 3 of winamp can't play a song bought on this service. Attempts to play a song in iTunes 4 that a friend bought required that I know his apple store login to play it as well.