I'd been using Aperture fullscreen prior to 10.7, so going in and out of it is long second nature to me. I also have most of the keyboard shortcuts memorized. The boxed versions of Aperture came with cardboard keyboard maps; very helpful, since it's Apple pro-software, and everything has a keyboard shortcut.
I have window-Aperture set up so that my secondary display (17") is mirroring the primary image, while the main monitor (24") has the window in browser mode ('v' to toggle between browser, viewer, and split). In full screen, I have this reversed, so that the secondary display is in browser mode and the primary screen is displaying my image as big as I can have it. I have the palate on the inside edge of the secondary screen in full screen.
The big draw is distraction-free editing. I do most of my organizing/reviewing/culling/metadata/exporting work in window-mode.