I've been wanting to get banks to implement this kind of thing forever. For instance, it'd be nice if I could log into my bank and set a url that they post to every time a transaction happens. Then I could set up a service at that url to take their message and do something with it (email myself, send an sms, automatically enter the transaction in buxfer, etc).
Same for statements. Instead of sending me an email, just let me specify a url. When my statement is ready, it's posted (in json or xml format) to a url I specify. Then I can slice and dice my own financial data and update my long term cashflow graph, or something.
Since the url is specified by me, while logged into my account (which should be secure), I have total control over who has my data (assuming DNS is secure and I provide an https url). If I wanted to use a service like Mint or Buxfer, I could add their callback urls to my account. When I decided to stop using their service, I simply remove the urls from the account. There is no need for Mint/Buxfer to know my login credentials or even what bank I use.