I've known about how selectors are processed for some time, I discovered it when I was looking into optimization strategies for JavaScript and figured I should look into how CSS is processed. I made a variety of tweaks, including finally just removing nearly all the CSS, and (somewhat disappointed) did not see any visible changes in the speed at which the browser rendered the page. Not even on IE6/7. Anecdotal evidence only, but to Jim72's point, I wouldn't waste time on it.