Believe me, it's much better than when Apple started, getting to have their cake (UNIX stability) and eat it too (with consumer OS functionality) has had the team split many times. I think you'll find that the trend is exponentially improving this exact problem with each release (something which I had hoped as focused an article would test). And, Apple is still working on it along with the Darwin community.
However, the good news is that at least Mac OS X has the multithreading potential to be leveraged, Windows is tapped out, meaning once OS X is on-par (maybe with Leopard, maybe with the next release), Windows will have to start looking to Blackcomb to improving.
I am much more concerned about Apple's OpenGL implementations when it comes to gaming... but that's also being worked on now too as Apple wraps up 2D and looks on to 3D.