I run Snow Leopard 10.6.1 on my Mac Pro, and saying that I'm disappointed would be an understatement.
The worst issue for me currently is the horrible wireless connection to my router; this worked great with Leopard and still works great with Vista 64 on that machine. But in Snow Leopard, the connection always drops or slows down to a crawl.
Then there are the compatibility issues. Montage still does not work at all and I don't need to repeat the list of known issues with other apps (like CS3, for example).
And besides everything that Apple's marketing machinery boasted about, there are ZERO performance improvements - rather the opposite. I think Finder is now slower than it was in Leopard, especially when you use the more detailed list view and browse through a folder with lots of movies or applications in it.
This "upgrade" is about to convince to cut my losses and fully switch back to Windows. It seems that besides nice designs and religious marketing, there is nothing more to expect from Apple anymore.