I've been playing around with Lion, Apple's new version of Mac OS/X. In general I really like the new features and will very soon be purchasing a Magic Trackpad to go with my iMac.
One feature that I can see myself using (if only to help me focus) is full screen applications. Apple added a little icon in the top right corner to all windows that allows you to make the app full screen. For applications that are full screen aware (like the new version of Mail) you just hit Escape or CMD-Shift-F and you go back to the windowed mode. However, for some reason, once you put Terminal in full screen mode it stays there for good. Even after you exit and unload the app (e.g. with CMD-q) and then restart. Neither Escape nor CMD-Shift-F seem to work to reverse the full screen process. Eventually I stumbled on the fact that when you move the mouse pointer up past the top of the screen, the menu bar appears (it may take a second). The menu bar now includes a new icon for reversing full screen mode. Hurray!