I've been using Windows 7 RC for several months and it's brilliant. As I mentioned in another thread, I haven't had any program crashes apart from one time very recently when my copy of Street Fighter IV gave up the ghost when it lost its network connection. The OS itself has been solid ever since I installed it and it's super fast.
I wish that I could say the same about Leopard, but ever since I got that I've seen the spinning beach ball, program crashes ("The application xxx quit unexpectedly") and the dreaded kernel panic WAY too many times.
If I had to rank all of the modern operating systems from the two companies, it would go like this:
1) Windows 7 = OS X Tiger
2) Windows XP SP2+ (but not earlier versions, they were what caused me to buy a Mac in the first place)
3) OS X Leopard
4) Windows Vista SP1+
Now, where does Snow Leopard fit into this list? Can Apple restore my trust and create an OS that is as stable as Tiger?