The reason Mint is doing so well is quite simple: it's so damn easy to use. I just signed up now, and I was expecting to have to go through a number of loops to get it to grab the data from my multiple bank accounts, but it was a breeze. Just another step in the sign-on procedure - truly great work on minimizing the number of people that default from linking their bank accounts. And the UI is goal-oriented with a dee…
Everyone, pay attention here. Mint doesn't have any technology. They're just an unbelievably well-designed front end for Yodlee. "[T]he UI is goal-oriented with a deep understanding of common tasks people want". Is your site doing the same?
Mint uses only your account login credentials for access to your account information and Mint does not store these credentials.
Clearly that information needs to be stored somewhere, but Mint can make it sound to the users that it is magically not stored (because it's technically not stored by Mint).
I haven't actually used the service. I have a general aversion to services that ask me for my password to a 3rd party account. The import-your-contacts types are bad enough, but bank account access is just too much for me to potentially give up.