I'm wondering how sites these days are managing their content and AJAX calls.

How is it that Facebook is able to have a URL like:
http://www.facebook.com/zuck

without with / on the end of zuck like
http://www.facebook.com/zuck/

This is obviously really handy as they don't actually need to create a sub-directory called zuck.

I noticed as well that places like http://hypem.com/popular is doing it too. Convenient for them as they're able to run their media player without breaks and they don't need to to have a # in their URL.