So far I'm favorably impressed with Leopard. Not bad at all for a new OS.
But I have run into a few minor problems too.
As IEatApples pointed out, Disk Utility won't repair permissions.
And the Dock won't redraw properly after running a graphics intensive game. I keep my dock at the bottom, and after running Jinni Zeala, the Dock icons are covered with green blobs. Moving the Dock to the side and then back to the bottom clears it up.
The Leopard installer did not retain my mail SMTP settings. I tried to send an email and the send button was grayed-out. After a little searching around I discovered that my outgoing server settings were blank.
Of course, Finder no longer automatically remembers window settings - it applies one setting globally, unless you goto info and check a button to always use a setting for a particular window. This isn't really a bug, but a feature loss.
Time Machine could use a few more user options, such as choosing the frequency of backups, having a backup now button, etc. Again, it's not a bug but a feature nice to have.
Overall though I really like Leopard. Can't wait to see what's in this first revision.