We have a large Confluence installation that serves the entire University of Illinois campus. When new users get started with Confluence, they often fail to notice the "Minor change" checkbox during page saves. This results in large numbers of email updates being sent to other users, who then complain (often) to me.
A co-worker recently asked if "minor change" could be checked by default, but of course that would lead to a different set of problems. As an alternative, I'd like to suggest that you remove the "minor change" checkbox completely, and replace it with two separate save buttons labeled "Save and Notify" and "Save without Notification" or something similar. I believe that this would be easy for users to understand, and would completely solve our "minor change" dilemma.