I just saw an interesting article in the New York Times called "A Company Computer and Questions About Email Privacy". The article is about a court case involving Scott Sidel and Structured Settlement investments. On one side is Scott Sidell who left the company and "found out that his former employer was reading his personal Yahoo e-mail messages, after he had left the company", ...including e-mail messages that he had sent to his lawyers discussing his strategy for winning an arbitration claim over his lost job." On the other side is Structured Settlement investments who say Mr. Sidell had returned to the office after he was fired and had begun using another employee’s computer.
The discussion was around that while using that other person's computer (at the office), he must not of logged off of his email account. I am not going to debate the he-said, he said - but I will say that this is a great lesson learned for all: LOG OFF OF YOUR DARN EMAIL ACCOUNT IF YOU ARE NOT USING YOUR OWN COMPUTER! Many email programs have special functions that allow you to stay "logged on" for a short time, without having to enter your own ID/password. This works great when you are using your own personal computer - that you no one else is using... But, if you EVER log on to a public or another person's computer to check your email - it is important to log off afterwards. The same goes for logging onto any other website where a user id/password is needed - what is also needed is to "log off" afterwards.
Even if you log off, your account can be compromised so it is important to be careful with what information you send via email. So the final lessons learned is to log off of online accounts after using them and save some information for a phone call!
Lifehacker.com has an interesting post about "electronic tripwire" in your email account to keep you aware of email break-ins.
Any others to add?