Simon Willison points a incredibly cool CSS site demonstrating the use of this technology to create beautiful and compelling sites. The site uses the same HTML document and applies five different CSS stylesheets to it that completely change the way the site is displayed.
I’d just make one suggestion to the site creator, tough. He could have named the stylesheets in the document to allow Mozilla users to change them with just one menu click. Anyway, the site is certainly worth a visit and some study.