The most annoying bugs I've found:
If you're using an app that hides the cursor, e.g. fullscreen videos in iTunes, or games like Minecraft, then swapping between spaces keeps the cursor hidden. The only way I've found to undo this is to activate Mission Control. Simple fix, but annoying nonetheless.
Activate Launchpad, highlight the dock, deactivate Launchpad into a fullscreen app, and the Dock is still there. The only fix is to activate Launchpad and un-highlight the Dock.
Safari in fullscreen is wonderful, but after having it open in fs for a while, closing tabs and using bookmarks gets messed up. >,<
I doubt you've heard this one, it's really obscure, but you can't freakin delete apps from Launchpad without changing system files. =P
Sometimes moving the cursor to the top of fs safari and then back down moves the whole window up, hiding the top of the window behind the toolbar, and leaving a little black margin at the bottom. Fixable by deactivating fs.