If I forget to log out, my account is open to everyone. If I forget to click "remember me", I have to sign in twice. Making systems that fail safely in case of human error is a good thing.

Although one of my favorite ideas was a system I saw at a hardware store. You could use their terminals to look up products. The terminals had a pressure pad in front of them, and as soon as you stepped off the pad, it ended the session, cleared the cookies, and logged you out.