Secondly, I would change the presentation of your "is it safe" FAQ. Yes, I am comfortable with Amazon or Gmail storing my information, putting it on the web. But why should I trust YOU? It may be abstractly safe, but what reassurance do I have that YOU won't rip me off?
And, finally, how will you do this? Are you writing adapters that call each of the relative services' API to update information? What about my local credit union without an API? Will you tell my grandma that I moved?
As a possible solution to the above, you might want to seriously consider tying in with something like PostalMethods' API (http://www.postalmethods.com/postal-api). There's an addt'l revenue source opportunity as well; have people enter the info of everyone they want notified, and you can send snail mail to those w/o an API.