[grundprinzip]

It's an awesome eye-catcher, they should make a JQuery plugin (if it doesn't already exist). And the code is rather (minified) simple:

https://gist.github.com/grundprinzip/5868304

[Killswitch]

No need for a jQuery plugin, it's simple to do. I noticed it too and looked through their JS and found it to be way more complicated than it needs, using jQuery.

http://jsfiddle.net/Killswitch/BSukL/show/

Nothing on the page but the code, so open that in a new tab and swap tabs to see it in action.