Detecting user changes on a form....

Question

I have a form with a tab control on it.  On each tab page I have lots of checkboxes which represent answers to questions that are presented to the user.

I only want to save what the user has answered and am struggling with a way to iterate through the controls on each tabpage and saving only what the user has answered OR HAS CHANGED, in which I would just update the database instead of "inserting" a record.

Any suggestions on detecting changes?

Thanks in advance...