Port Based Authentication (Dot1x auth)

Most of my study time the last few days has been devoted to Port Authentication using dot1x (802.1x). Going to my BCMSN book was honestly not a lot of help since it appears the CCNP only requires you to know how to set up the simplest authentication, only for wired, and only the switch commands. I will cover, perhaps a bit more than the switching exam expects you to know, but it is an involved process so it will still be an overview.

Why do you need port authentication? Well suppose someone brings in a laptop from home full of virus', or a malicious user decides to unplug a work computer and use the network cable to plug in their own laptop to attack your network. (I know everyone has perfect, aware, tech savy, completely trusted employees and users, but this is just theoretical)