I know I'm way behind on this but there's one thing I noticed at the end of Macword's "Close-up on Aperture":

• By the way, there’s no Save command in Aperture. As you make changes, those changes are recorded in a SQL database.

Expect to see a lot more of that as applications take better advantage of CoreData and/or provide built-in versioning systems for their files. When you think about it, why should you have to remember to save instead of just having the ability to undo as far back as you like?