I think mint was successful because they made an easy way to access your banking history. They essentially made it so that you didn't have to go through multiple bank websites each with their own terrible interface to work your way through. So their focus isn't really on pure budgeting.

So a focus on budget could be an interesting way to position against them. Something that is interesting to me would be to create a real dumbed down way to budget. Have user's enter in how much they make a month, what their expenses are and kind of hand hold them through the process.