Apparently, facebook keeps track of all the profiles you view, and it stores everything ever put on facebook (even stuff you delete!) There's also a master password that lets you access any profile on facebook.
"I’m not sure when exactly it was deprecated, but we did have a master password at one point where you could type in any user’s user ID, and then the password. I’m not going to give you the exact password, but with upper and lower case, symbols, numbers, all of the above, it spelled out ‘Chuck Norris,’ more or less. It was pretty fantastic."Crazy.