For online applications such as Mint and Quicken (online), to automatically update your accounts, they'll always ask you to enter your login info to your banking and/or investment accounts.
Do you trust giving out these types of personal information, how do you know you can trust them?
Moderator's note: I've merged into this question the following similar question (and its answers):
Services like mint.com and quickenonline.com they seem to simplify money management and offer an attractive alternative to using traditional financial software. I'm tempted to use them, but security is a definite concern. What are your experiences and thoughts on this? [this version was originally asked by M. Attia]
(Moderator's note: Intuit, the makers of Quicken, acquired Mint.com in September, 2009.)