Monday, January 18th, 2010>p>Geuis Teses has released an enjoyable library called Helium that has the goal of testing your stylesheets for unused style.
You inject helium into your site (e.g. put it in an included footer) and then when you hit the first page you will have a popup asking for the pages you want to test. Helium will find the style sheets that you use and will store that information and the page information inside of localStorage. Then it will XHR around (so your styles need to be on the same host), test each page, and finally give you results.
I put up a trivial example to give it a ride and ended up with:
I ran into a minor issue with regards to relative stylesheets so I did the Github thing and forked, fixed, and pull requested. I love Github :)