Are there any utilities that will crawl a site and determine which css rules are in use and which are not? We have a large site and a huge CSS file (--don't blame me I just got here). And, I think much of it is not being used however I'm afraid to strip stuff out just in case.
The file is confusing and difficult to manage and I think if we can trim it down by getting rid of the unused rules we will have a good starting point to go through and try to make it better.
Try the Dust-Me Selectors Firefox extension by SitePoint. It finds CSS selectors whose rules are never applied to your pages so you can remove them from your stylesheets.
I had the same problem a while ago (5k lines in a CSS) and found this Firefox Plugin which worked very well for me.
The Google Page Speed plugin for Firefox's Firebug addon is also a great tool that will highlight the unused CSS selectors as well as inform you which ones are poor performers.
As always though, you need to be aware that the CSS selector may not be used on "this" page but may very likely be used on another page so be careful when pruning them to ensure they are truly unnecessary.