You may have heard about Lion’s new Versions feature, which is currently supported by iWorks apps and Preview… but have you tried to use it yet? If you haven’t, chances are you won’t find it right away even if you look for it really hard. To use Versions, you must first open the document/file, click on its name in the title bar, then select “Browse All Versions”. This will take you into Apple’s Star Field interface (think Time Machine), where you browse the different versions of the document/file.