Edward,

>IMO, it doesn't matter how a user will perceive saving data.
Aks a beginning user. Sit beside a real beginning user and let them play with WORD, EXCEL or some other program and learn. I think (Like Cooper) that your program is capable of handling unexperienced users. Things that are probable should be done automaticly (like saving) and things that are possible (like undo) should be done explicitly.

>It's much more important to design the interface that any changes which are seemingly important for a user, will not require any serious changes in code itself, i.e. any (even most fanciful user's request) will be done quickly and users will be happy. How it's usually done. You separate interface from data and move all 'save_data' related code to generic method and after this you can call it from any place you want: button.click or form.destroy or form.keypress or navbutton.click etc.

These things are not mutual exclusive. They may well go on together. By using OOP strategies things like choosing between Implicit and explicit save should be no more than setting a checkbox in the options dialog.