Some of us have Command-S wired into our hands. Whenever we write a few words or enter a couple of cells into a spreadsheet, our hands twitch and we compulsively type a Command-S to save a document, just in case... A new feature of OS X Lion is Auto Save, which is going to stop a lot of Mac users from doing the Command-S twitch. Versions is another related feature that keeps copies of different versions of your documents for posterity.
Auto Save takes a snapshot of whatever you happen to have open on the screen in an app at any particular time, and saves it for you. Let's say that you have TextEdit open with three different documents, all scattered about on your 27" display. None of the documents have been saved, and you suddenly realize that you need to leave for a meeting. You quit out of TextEdit, and the familiar "Do you want to save the changes you made in...?" dialog doesn't appear. No problem. The next time you launch TextEdit, all three of those documents open up in the exact same locations on your screen that they were in originally.
Another cool feature of Auto Save is the ability to revert to a last saved version of a document. That's helpful when you're working on a document, add a lot of changes, and then suddenly realize that what you've added is ... crap. Just select Revert to Saved or Revert to Opened from either the File menu or a disclosure triangle next to the title of the document, and you're back to your original document.
What's fascinating is that Auto Save and Versions keep all of the different versions of your document in one file. There's no folder full of saved versions with time and date stamps -- instead, you just see the file and all of the magic is done internally.
What if you don't want a file to be accidentally changed. That's where the Lock feature comes in handy. Two weeks after the last time you edit a document, Lion auto-locks it for you. The next time you try to make a change, Lion asks if you want to unlock the file or duplicate it to create a template.
Versions brings the power of Time Machine to individual documents. In many Lion-savvy apps now, there's a "Save A Version" menu item that takes the place of the previous "Save" item. This is where that muscle memory that you built up doing Command-S is going to come in handy. As you write a document, you can continue to use Command-S from time to time to save a version of a document. When you want to go back to a previous version, choose "Browse all versions" from the drop-down menu near the title bar of the document and a very Time Machine-like window appears:
The Versions window provides a side-by-side comparison of your current document version with all of the other saved versions. If you find a previous version that you want to copy something from, just do a copy and paste between the two. There's also a Restore button for making a previous version the "live" version of a document.
At this time, Auto Save and Versions are only usable in specific Apple apps, including iWork 9.1 (Pages, Keynote, and Numbers) and TextEdit. As more apps are updated to take advantage of the many new features of OS X Lion, we're sure to see the convenience and security of Auto Save and Versions become commonplace.