You may be asking yourself why I've even bothered looking at other operating systems if Linux with an accompanying distro does everything I need. The answer is that Linux has two main problems that have been driving me crazy lately--no glitch free audio and terrible responsiveness when copying large files.
The audio problem is well known, and efforts have been underway to address the issue. I think the Linux audio playback is getting better now with PulseAudio, so this issue doesn't bother me as much any more.
The disk io responsiveness issue is less known. The issue appears when copying lots of or large amounts of data on a 64-bit kernel. The kernel load escalates to the point the system is unresponsive ( the load climbs up to 9+ on a beefy machine with a single copy command running). This is the primary reason I started looking at other operating systems.
A few days ago, I came across this linux kernel bug entered over 2 years ago. Interestingly enough, the load only escalates when I boot up using a 64 bit kernel--the 32 bit kernel is fine. I'm planning to jump onto this related kernel bug and see if I can offer testing or other support here shortly.
Follow up 1/14/2009: Looks like there's some progress on the performance bug. A Slashdot article here explains more.