When I first read the keynote my first thoughts are that it will be implemented using a versioning file system, something like a system wide version of CVS. Until I read about this... http://www.apple.com/macosx/leopard/timemachine.html So let's say I import in some photos into iPhotos at 2pm (with the delete originals option checked!), then absent mindedly deletes them at 3pm, what good is time machine going to do for me? Nothing. Likewise for a Word document that I started on this morning, then sometime later at night at 11:59 when I'm really tired I accidentally selected all text and overwrote it with another character. At that moment word autosaves. What will time machine do for you? Nothing. Suddenly I'm more interested to see how Microsoft will try to do their implemented. They might have failed with WinFS, but at least they dare to think different for once and push technical barriers. Spotlight? Time machine? Nice brand names tacked onto what's another background service in Microsoft's world.