Has a friend ever asked "Can I borrow your laptop to check my email?" Maybe you're uncomfortable handing over your account to them. There's a simple answer for that: the guest account.
Guest accounts are available in Fedora 15, but are disabled by default. You can activate this feature by installing the xguest package, which is easy enough to do by going to Activities - Applications - Add/Remove Software.
The Guest account doesn't have a password. Also, any files created there (including saved passwords from the browser) are deleted automatically after they logout, so it's great for short-term use like checking email or quickly updating their Facebook.
There's more about guest sessions and user management on Fedora 15, at LinuxBSDos. The article has a lot of information about account management in general. It's pretty straightforward, but screenshots are always good.