@Puerto: Yes, I have noticed improved sound quality with Macs using Snow Leopard. I do not understand why, and it doesn't seem to work with all systems. If you upgrade, let me know your experience. I'm always wanting to know what other people think.
As for Apple NOT "bragging" about improved performance, that is par for the course. Apple completely rewrote Snow from the ground up, and there are several improvements that can be found throughout the OS, but Apple only touches on items that people will notice the most. Subtle sound quality differences are not important to anyone except "audiophiles" and professionals, so Apple doesn't make a big deal about it. I do know people in the professional AV studio market that openly talk about the differences, so others do notice it. I know that some USB and FireWire interfaces work and sound better with Snow, but again, these are subtle and only noticeable with certain applications.
Please keep me posted. I use this forum to learn about new and better solutions. I don't have all the answers, but I try my best to have the right questions.