I'm surprised Mint was successful at all, given that you have to give them your financial account login ids and passwords to use their system. Storing such data centrally seems like a big risk to me.
They don't store it themselves; they use Yodlee to actually store everything, and Yodlee is the one that actually has done all the work (and it's a huge undertaking) to keep everything secure.
With all the writing about this deal and what gets stored where I think yodlees' profile in the blackhat community has risen considerably in the last couple of days.
