Money Thyme sounds nice, but something about letting a third party app have access to all of my financial info is kind of scary to me, lol. I'd need to understand how it works before I'd use it because I don't remember Mint having an API.
It doesn't take much digging to realize that people have been reverse engineering Mint's API to get it to work for them...
Early Look at Mojito: Mint.com for Windows Phone 7 - Matt McCormick
https://satisfaction.mint.com/mint/topics/an_api_for_manipulation_of_personal_data
Don't get me wrong - I share your caution. I also have my reservations about putting a username/password into an app where I don't know what is being done with that username/password, when it involves my money. But if all they have access to is the Mint user/pass, I'm thinking you're at least safe from being cleaned out (assuming you don't use the same user/pass for mint as you use for the bank). I know I don't use Mint's full capabilities, but can you remove money from an account with it, or is it read-only on the bank accounts? I know I've only used read-only functions, so I'm not sure any action functions exist. I know - someone could see what you have, but at least you'd still have it.
I'm thinking I'd want an app like this to go through some kind of certification process. And hey, while I'm on that subject, I wonder just how many people installed the Bank of America app (or any other app) and didn't check to see who published the app? Hmmm... There's no Wells Fargo app. Maybe I should publish one really quick, if you know what I mean.... No, I'd never do that, but I'm saying it to raise people's awareness.
Still, the question remains, what kind of assurance can a developer give that his app is not sending your username/password home to Papa, and that your money (or email, or twitter account, or whatever else it is you're trusting to a developer) is safe?