Article SiteThis article discusses the use of multiple style sheets rather than one large one. The main advantages really only matter if you have an extremely large CSS file with thousands of lines.
The author discusses breaking your CSS file into type, layout, and color files to organize them a little better and make it easier to find your way around the document easier. He recommends going even further and making CSS files for each kind of media, whether it be print, screen, or mobile.
The article then goes on to discuss how to make your CSS files invisible to older browsers such as IE5 & 6 and Macs by using tricks that only certain browsers recognize and others ignore.
Overall this is a very informative article and I would recommend it highly if you are dealing with large CSS files that get a little tough to navigate through.