Mint.com is built on Yodlee's banking-data platform.

http://www.yodlee.com/index2.shtml

You can check out Techcrunch's view on Mint's use of Yodlee's data here:

http://www.techcrunch.com/2009/09/18/mint-is-yodlees-youtube...

Personally I think that such insane attention to detail on the user-interface is admirable and he definitely deserves the sale.