Rated 5 out of 5 stars
Just to add to my previous review. I tested this pluggin along with the app described by Alex called JClaim (check a few posts below to find a link).
After installing JClaim, you will find an option under General - Handy Tools - Clean CSS. This tool is used in combination with the Dust-Me Selectors plugin.
First you need to use the plugin on a page or site. Next you save a .csv file of the results. In JClaim, select the .csv file and the .css style sheet that you want cleaned (that was analyzed initially). Press 'GO' and you will be given a newly formatted and cleaned style sheet in the textbox. Great!
Copy and save this as a new style sheet so that you don't lose the original. Now you can replace this style sheet on your page or site and check to see if everything still displays properly!
My experience with this process is that it did seem to remove unused styles, however, you will need to go through the new style sheet to ensure that everything has been formatted properly. My page did not appear properly at first but then I realized that certain style definitions had spaces and commas where they didn't need to be. It might help to use compare software at this point in order to compare the old and new style sheets to help you find formatting errors.
Hope this helps and Good Luck!