You are far more likely to have your information stolen by something that gets on to your computer than someone getting into mint. They use security equivalent to what your bank uses.
Also, if you don't like getting emails about your credit card balances you can turn them off. I personally don't have a problem with it, what is somebody going to do with that sort of information anyways?
Banks have been hacked, the point is there's no real way to quantify how 'safe' their service is. If you want to use it and all of it's great features it comes with a risk.
I personally just didn't like getting those emails, it opens up another potential way of someone getting at your personal information through a less secure source, email. I don't know what someone may be able to do with the information, but it's a starting point for building a profile on you.
I never had a problem using Mint, but it can't reconcile a lot of my CC & bank info so it was useless to me. I'm still open to a security risk because I use each of my accounts online so there is no 100% secure way to do this
