There's obviously security concerns with ANY system that has your information...but I just don't get the specific concerns with Mint. I also don't understand what real world implications a hack would really have.
If Mint itself was hacked, they could see how much I spend on stuff and how much debt I have? I guess that could be awkward for some people (online porn or gambling transactions maybe?)
If they actually gained access to my usernames/passwords, they could log into my accounts. Then what? Mail a check somewhere? Do a funds transfer? Now they've given a paper trail and account information. Seems like an easy way to get caught.
My information is already a million different places. Experian, Transunion, Equifax, US Department of Education (student loans), Social Security Administration, IRS, Vanguard, Chase, Citi, Discover, etc. They could all be hacked too. Some of those pose a more serious risk than Mint getting hacked.
Maybe I'm just naive, but I'm not worried about Mint. I check my credit reports a few times a year (so I'd notice any new accounts easily), and login to online banking at least twice a week so I'd notice any odd behavior. The credit card companies text me when transactions above a certain amount go through.
To be honest, I think someone leaving a company laptop in a taxi with unencrypted information on it is way more likely than a Mint hack.