a good article and advice here....
This is a bit scary:
Using Wi-Fi? Firesheep may endanger your security - CNN.com
I'm sitting in a coffee shop. At a table against the opposite wall is a guy named Michael C. I've never seen him before. However, I know his name (including his last name, which I'm deliberately not saying here) because right now we're using the same Wi-Fi network and he's logged in to his Facebook and Google accounts.
This means I'm also logged into his Facebook and Google accounts, although he probably doesn't know that. If I chose to, right now I could read and delete his private messages -- or send out messages from his accounts. I could even edit his account profiles, alter his privacy settings or forward all his mail somewhere else.