Just wondering, because it seems that if they have access to all my information, then there's the possibility that someone on Mint's end can steal money, even if it's one cent per month per user, which could add up with millions of users.
Yes, there is such possibility. Also, there's a possibility people made your computer, your operation system, your browser, etc. put there some code there that would intercept your communications and steal your money. So could bank clerks (and unlike all other examples, this really happened in real world, numerous times, though usually at smaller banks), ATM makers, etc.
In the modern world, you rely on things made by thousands of people, this is a part of modern world's conveniences. You don't have to use it - you can store all your money in a big jar in your basement and nobody but occasional thief breaking in could take it.
However, fraudulent unauthorized transactions in most banks can be rolled back, and any transaction is reported to you. So fraud from mint.com people would be quite low on my list of risks.
Much bigger risk is that somebody could break into mint.com servers and steal information about your accounts from there or install some malicious code. I believe they have good protections, but no security system is perfect. You need to evaluate how the convenience of using mint.com compares to your personal feeling about this risk. If you feel you couldn't sleep at night knowing somewhere out there there is information about your money - don't use it. I don't worry about it too much as I know the chance of it happening is low and the chance of getting the money back if it happens is high, but if you feel differently - don't do it.
So could someone working at your bank directly. Of at your HR department at work. Most of the wait staff at the restaurant I ate at technically had access to my credit card and could steal money. While you are at work, someone could break into your house and steal your stuff too.
The point is, Mint and everything else is a matter of the evaluating the risk. Since you already understand the vulnerability (they have your accounts) and you know the risk (they could steal your money) what are the chances it happens?
1.) Mint will make lots more money if it doesn't happen, so it benefits Intuit to pay their employees well and put in safeguards to prevent theft. Mint.com is on your side even if a specific employee isn't.
2.) You have statements and such, so you can independently evaluate mint. I do not just trust mint with my stuff, I check info in Quicken and at the bank sites themselves. I don't do them all equally, but I will catch problems.
3.) Laws mean that if theft happens, you will have the opportunity to be made whole.
If you are worried about theft, don't trust other people or generally get a bad feeling, don't do it. If you check your accounts online with the same computer you log into Facebook with, them I would suggest it doesn't bother you. You might have legal or business reasons to be more adverse to risk then me.
However, just because somebody could steal your money, I personally don't consider it an acceptable risk compared to the reward.
I will also be one of the first people to be robbed, I am not unrealistic.