Andy Pedisich wrote a nice article The Truth about AutoSave in Lotus Notes/Domino 7, where he mention that you must be aware, that this feature must be setup at two places – on the client side and on the designer side as well. He mention that each form you want to Autosave enable must have this feature checked in his properties.
But he didn’t mention one big problem, which could be there. Because when you recover your autosaved document, this document isn’t new, so when you use NotesUIDocument.IsNewDoc it’ll return False. If you want to check if this document was recovered, you should use the field $AutoSaveRecovered in QueryOpen event or PostOpen event (this field will be deleted after PostOpen event). Also there is interesting field $DontAutosave which is used for temporarily disable the autosaving of document.
You should also take a look at great article All about AutoSave in Lotus Notes/Domino 7 at DeveloperWorks.