The stack frame now has a attractive border between it and the shadow which looks quite nice. Also, an option for folder actions now appears in the Finder's contextual menu.
There's a cool feature in Safari that lets you create a note from any selected text. I'm also happy to see that the Image Capture app no longer looks completely out of place and matches the other apps. Also, Preview's "Contact Sheet" view is very cool. Think of a PDF's pages being displayed in a big grid.
What's very nice to note, and what I'm most looking forward to, is the list of apps that Michael describes as looking the same but operating much faster, including Address Book and Font Book. I love what Apple's doing with this update in tidying up Leopard and making it tighter, faster and more efficient. I can't wait to buy this.