Not only is OS X GOOD, but...
...according to this study, it's the BEST when it comes to latency.
Disclaimer: I am not a music professional.
However, it seems to me the only problem with Mac OS X and music right now is the lack of software.
This story reports about a study done by the Peabody Institute which concluded that Mac OS X was the best OS ever in terms of latency through its CoreAudio system.
Two Linux setups performed better in the testing than OS X when the machines were idle, but when the machines were placed under a heavy load, the OS X machine did not significantly decrease in performance.
Now, switching gears: I also remember press quotes from Bias claiming that there would be possibilities to do things never before possible. When they originally released Peak DV in 2001, they talked about being able to have Peak and Deck running simultaneously on different channels with absolutely no performance loss in either program.
Again, I'm not a music professional, so I may be remembering that wrong.
At any rate, when things become available, and developers begin to be able to exploit X, rather than just 'get their stuff up and running' on X, I think it's going to be, like, 10x better than any OS has ever been for Audio production.