There are solid laws and remedies in place for when someone steals money from your bank account. This happens all the time at banks and they just replace your money without even telling you. Mint and Intuit have every incentive in the world to protect your money.

Giving out your twitter/facebook/gmail password is much more dangerous because there are no easily enforceable laws in place for when someone spams all your contacts, damages your reputation, or locks you out of your web accounts.