Maybe constituents could log in to a portal online that allowed them to see their own details.  They could then update them, make payments etc. etc.  saving would, of course, fire off an email to let the back office know and control any issues.

They could then update their mailing preferences so that a link could be placed on the bottom of emails for them to update preferences rather than simply opt out of everything when that may not be their desire.

The more that our supporters can do themselves the less time consuming it is for us: leaving more time for the important stuff.