After finding all the "broken" and regressed things from Leopard, and realizing how much I am NOT using most of the "new features" (from a UI standpoint), Tiger is looking better and better. I don't mean to undermine Leopards inner-workings, either. Snappier window response, networking and improved ichat/mail ARE appreciated... "Spaces" I had in Tiger with a 3rd party app (that had killer transitions btw), and additional Photobooth effects along with Time Machine aren't important enough to me.
But, the particular sore spots for myself:
Dock - option for nestled folders
Stacks - stationary icons that don't change with new apps and downloads
Finder Icons - less homogenized more visual diversity
Spotlight - Used to be simple and organized
Front Row - lost the "zing" with UI and transitions
Front Row - Re-integrate with itunes - and keep playing when it's activated.
Broken Widgets
Broken Apps
Firewall - Seeming too "dumbed down" or neutered
Login - background looks "cartoony" miss blue
It seems the very things that drew me back into the Apple world with Tiger - are being cluttered, blended and muted with Leopard. I give the new kitty until 10.5.1 to fix at least 1/3 of those problems - otherwise going back to my old kitty.