Insalled Snow Leopard last night on the MacBook.
Apple apps feel like they boot faster, but not by much.
Spaces seems to work a little better with PS.
New Exposé is wonderful as is Dock Exposé.
Not sure I can feel any difference in Finder, but I haven't had the chance to try live previews yet.
Stack navigation is awesome, much better than going into a stack only to have the stack open a Finder window.
Quicktime upgrade now does video screen capture

I wanted a free app for this about a week ago and now I have one built into the OS!
I miss my British flag in the menu bar

I have one negative point, if I wanted to look at a picture off the forum (or anywhere on the web) in PS, I could drag it out of the browser and drop it on the PS icon in the dock. This would either open the pic in PS or Launch PS then open the pic. When finished I could close the picture and it would just go away.
This no longer works, now I have to drag the picture onto my desktop, then into PS which leaves a copy on my desktop that I have to delete afterwards.
It's a minor point but something I do quite often.
I did use the option of better performance when on the power adapter and better battery life when running on the battery. These options have now gone and I can only hope Apple set it up the way I like it.
Overall, with limited use I'm happy but would like to see a couple of my options return in 10.6.1.