In this first developer preview of Snow Leopard there isn't anything that really stands out yet, except that System Preferences shows whether or not the system is run at 64-bit (probably part of Grand Central) and some apps have been updated (Address Book is 5.0, Mail is 4.0, Photo Booth is 3.0, etc). And it's official: Snow Leopard is 10.6
It's interesting to note how some apps were already being worked on by the end of May this year.
Screenshots from OrchardSpy
And just for fun: if get screenshots without the title bar (Command+Shift+4) and change its icon and file name and you can say to your friends, "Look I have Snow Leopard" when you really just have, well, Leopard.