autosave in osx lion
Since Lion testers are under a non-disclosure agreement (NDA) it may be difficult to get a definitive answer on this here.  From my reading of what has been released so far, and reading between the lines to Apples intent on bringing iOS (and in particular the iPad) functionality/experience to the Desktop, I would say that the Applications written for Lion will use that feature, and it will not be able to be turned off.

I say this because I think that the autosave and version system will be deep in the guts of the OS and once an application is written to use this feature, it won't be an option.

That's not to say that people won't find a way around it.