I think a lot of people would respond with something like "you use bank machines and online banking, don't you?" That is the same reason I hear people supporting voting machines and even online voting, but the problem is that there are significant differences.
Take a service like mint.com compared with your bank for example. The bank is a regulated company with insurance to back up your money should they make a mistake. Even if someone steals your debit card and drains your account, you will usually get all your money back. Banks have deep pockets and even the government has a vested interest in making sure the banks stay afloat. When they do make a mistake (and they will) you are usually quite safe.
On the other hand, mint.com is a third party that you are just going to hand over your bank passwords to. I think it is reasonable to ask:
- What kind of insurance do they have?
- How do they store the passwords? Is it on their own servers, or are they authenticated through the banks servers?
- If an employee of mint.com got into your accounts and sucked them dry, how long will it take to clear everything up from your point of view? Will the account be locked for months?
I am not saying not to use mint.com, but it is certainly reasonable to ask these questions.