3 Things
1.) I'm not sure if this was present in Leopard, but I just did this by accident a minute ago. Holding Command+Shift and pressing the pill button in Finder toggles thru the different view options for the buttons (ie small, larger, with text), and just holding Command goes in the opposite direction.
2.) When using extended mode, dragging an item from a browser (ie an image) to the non-main display (the one with the menubar), it will place it on the spot. In 10.5 when you did this it would place it on the main display, and then you could drag it to the other one.
3.) Maybe it only did this to me (WHY ME??), but regarding the awesome app GimmeSomeTune, it only changes your status to the current iTunes song when you have chosen the "Current iTunes Song" status. Before, it would change my status to the current song, no matter what available status I had set.
Also, when I first booted up, I was blown away at how fast was Safari was. So fast that I changed it back to my default browser. Now, however, it takes a long time to respond when I open a new tab. I was glad to hear about the smart eject feature, however I currently have a disc image that refuses to eject because it is in use, yet it does not show me what apps are using it.
BTW, Seeing as somebody noticed the Spotlight icon slightly changing, I can't believe nobody has mentioned this but the x-+ buttons look slightly different, not as sharp, I like it.
There's plenty of good and bad already, but Snow Leopard just came out, I can't wait for future features and updates to fix bugs.