If you use gmail, all of your email is probably going unencrypted over the Internet, allowing fairly easy snooping of all your sensitive data. You may feel good that there's an "https://" in your address bar after you type "gmail.com" into it and hit enter, but notice that after you authenticate and start reading email, it's gone back to "http://".
It's been possible for a while to work around this and use https even for email content if you knew what to do in the address bar, but now gmail has made it easier. There's a new option in the main Settings screen called "Always use https". I strongly encourage all gmail users to turn this option on.
It's still really lame that they haven't made it the default mode of operation. Come on, gmail, don't you care about privacy?