I've playing around with other CMS systems lately to get a feel for what is out there. I recently had the opportunity to hack around in WordPress and ran across a neat little utility in some of their docs. It is an external Online CSS Optimiser/Optimizer that does some CSS compression. Well, I'm always one to try something new so I threw in the CSS from this site and plopped the results into my theme's style sheet. Although I didn't notice any super speed ups, the code did compress 37%. Some of the options messed up my site so I recommend testing out each before using the results. Let me know if you see something odd.
Playing around with the CSS made me run the standard XHTML validator (see link in my footer). Sadly, my site didn't validate. Doing some checking, I found it was something I'd run across before. I'd blindly copied YouTube tags into my articles which won't pass XHTML standards. Fortunately, it was an easy fix and all is well!