It’s hard to reproduce, but I occasionally find that my Dashboard/ExposÃ© hotkeys are still disabled after exiting full screen mode. In the Dashboard and ExposÃ© System Preferences Pane, all the hotkeys have been reassigned to… nothing. Alt-tabbing, on the other hand, is always restored after full screen.
My two cents: I really prefer the old Scrivener Gold approach, which lets you alt-tab and ExposÃ© to your heart’s content.
(10.4.7, G4 PowerBook.)