I do not think Autosave ruins documents, but it definitely ruins the workflow of a lot of people -- not just of power users, but of everybody who handles documents of a complexity higher than one's memory span (i.e., writing seven words, plus or minus two, in a document). The idea to copy the behavior of an iPad to the computer is fundamentally wrong in this case because an iPad is not a computer: you don't write a book on an iPad, you do it on a computer (for a similar way to copy the wrong model, carefully inspect the differences between Lion's Address Book--almost useless now, as it copies the physical characteristics of a physical address book, including all its limits-- and Snow Leopard's Address Book, which at least had some usability. Now if you look at groups, you can't look at individual addresses, and vice-versa... because in a physical book you can't do it and so let's regress a computer back to when there was no computer, so that people will be less confused . Call it progress.... ).
What should be done to make Autosave become tolerable, and perhaps useful in some cases?
1. It should become a per-application option, minimally; ideally, a per-document option.
2. Versions should include version changes highlights -- as in "Track changes"-- with respect to the current manuscript version.
3. "Revert to save..." should let you go back to the last saved version BY THE USER, and not by Autosave, so that you can always go back to the version YOU saved last.
4. "Revert to save...." should be "undoable", so that if you don't like the last version YOU saved, you go back again to the version with the latest modifications (Believe it or not, "Revert to saved..." is not undoable right now, so that if you go back to a previous version, you loose track of your own changes.
5. Changes during versioning should be fast enough and unobtrusive enough to allow people to really work smoothlessly -- the test case here is Keynote, with its presentations that can be really very big (in my case, when I teach, I have presentations that easily go beyond 200Mb).
The point of distinguishing saved versions by the user and saved versions by the computer is a really fundamental distinction. The computer saves things arbitrarily (in this case, every 5 minutes). The user saves changes in a meaningful way: s/he saves what she WANTS to save. No OS can substitute the intentions of the user! Right now, with my trial-and-error attempts, I have not seen a way to distinguish what I want to save and the arbitrary saves done by Autosave (I may be wrong).
Short of these requirements, I really think it is doing much more harm than good to anybody minimally using a computer to do real work. Anybody sees anything else? Let's hope somebody at Apple reads this.
l.