Cookies are not even needed, simple Javascript will do for just switching if no remembering is required. I know how to do this
However, I still think that browser implementation would be more reliable and better solution for both users and developers. For example - when you want to accomplish this wiht Javascript you have to provide switching buttons/links in every page. But that gives developer one more element to host on his pages, element, that is not content-related. Thats not nice. Browser should be taking care of stylesheet switching. After all - there is perfectly standard way to add alternate stylesheets and this has been possible for long time now. Just makes me wonder why CSS-compatible browsers havent implemented it yet.