This is a really fantastic idea... I love it. I didn't sign up though, first the site doesn't give me any confidence that my information would be safe with you, and It doesn't tell me how I can be sure you updated my information. I think a better design, and some more up front info on how it works would really improve it. Once again though, lots of potential with the idea.
Enumerate all of the methods/protocols/whatever that you employ in keeping our information secure. Most (all?) of the site seems to be behind https, so that's a decent start. Are you PCI compliant? How to you store and encrypt our data? Obviously, you don't have to divulge the secret sauce here, but something more than what the FAQ outlines would be a good start. 37s has a decent go at a security page: http://37signals.com/security