InfoWorld review: Mac OS X Lion, more than multitouch

Lion apps can enable two framework-based file protection features: autosave and versions. Autosave is self-descriptive, but instead of saving once every few minutes, Lion's autosave works constantly in the background to keep the data on disk in sync with the documents on the screen. At shutdown, apps that implement autosave can save open documents without asking whether that's what you want. Lion can also terminate a long-idled application if memory gets tight, but only if the app opts in to this behavior.

In an app that supports versions, every time a document is saved, instead of overwriting the entire file, Lion invisibly records only the changes made since the previous save. Option-clicking on the file's name in the title bar pulls down a menu that lets you display a Time Machine-like interface to browse through all saved versions of the file. The current version is presented side by side with any historical version you choose. You can revert the entire document with one click, or copy and paste contents from one or more older versions into the new one. You can see versions in action in TextEdit.

Versions works transparently, but you can easily tell if an app implements it: The File menu's familiar Save As option is replaced with Duplicate. Note that the Versions feature does not save the incremental changes in the document file itself, but to an invisible folder on your startup disk. Thus if you copy the file to any location (via the Duplicate command, in the Finder, or by emailing it), only the final version of the document is sent. That means no one can inadvertently see your changes, but it also means you have to keep the file in its original location to have the previous versions accessible to you.

Finder has undergone a fairly extensive overhaul. One new feature that can catch you off-guard is the new All My Files view, which is shown by default when Finder launches. This creates a list of all user-related files on the system, ignoring folder hierarchy and bundling them instead by selected criteria, such as kind, application, date, or label. If Grouping is selected in icon format, each group is shown as a scrollable row of icons.