OS X - at least in theory- should be good for musicians. However the conversion of music apps has been a bit slow. My understanding is that some of the music support (at the system level) has been being introduced slowly through the upgrades. Thus the music app developers haven't been fully able to get their programs up to speed. Digital Performer for OS X has been announced but won't be available till later this year. I keep hearing good things about Sonic Foundry's ACID. Obviously I haven't had a chance to check it out.

Before they made me they broke the mold!
http://home.roadrunner.com/~kflach/