It never ceases to amaze me how many people share passwords with friends, co-workers, or significant others. I have never shared a password with anyone for anything.

The first time I ever got a UNIX account (back when those were hard to come by), my friends impressed on me the importance of locking my screen every time I got up from my computer and never giving anyone my password. Granted, their example was a little bit silly (they said, "someone could use your account to email president@whitehouse.gov with a threat and the FBI would come knocking on your door because it came from your account."), but with your userid and password someone can do anything they want and it looks like you did it.

This is like the first thing they should teach in any basic computer class - never share your password for any reason - along with some real-world examples of why it is a bad idea.