With Windows 7 64bit out in circulation, there's been a lot of conversations about the differences in user experiences between Snow Leopard and 7. Here's a great synopsis from Adobe's Dave Helmly:
"I will say that Windows 7 64 is has been a huge hit for editors. The biggest difference performance wise between Mac & Windows has been in the area of graphics cards. Apple does not really allow 3rd parties (nvidia/ATI) direct access to the OS for certain calls to the GPU - what does this mean? It means that they can't do a lot of tweaking of the video driver like they can on Windows. Nvidia and ATI release lots of driver enhancements for Windows each year. The difference it not huge, but is noticeable."