LinkI saw a pic of the thing. It looks like a keychain fob or USB stick. It has a small screen and a single button. I think it was said Blizzard will sell them for $6.50.
Here is how it works: You set up your account and opt-in to using this doohicky. Your account is then tied to the serial number on the thing. This serial number is tied to an internal random seed that is specific to your unit. Whenever you click the button, it does some funky math with the random seed and the current time as variables, then spits out a number. You have to type in this number along with your username and password to log in to WoW. The server knows what number to expect based on the same parameters (current time and your fobs serial number).
I guess this is neat if you're really worried about someone stealing your account, or you have other people using the same computer on multiple accounts and you dont want them using yours. Even with a keylogger, since the number you type in is always new, it becomes useless.
Maybe a little overkill, but at least it seems cheap for those that want it.