You should not disable cache permanently. Once all css changes/edits are complete you should reset the skin guid so that all browsers will be forced to load the new version of the css. The browser caches based on the url so the guid appended to the url makes it different therefore it will load it and then cache it again with the new url. The cookie is just for temporary for while the designer is working so he doesn't have to keep resetting the guid after every edit but once he is done editing he should reset the guid and disable the cookie.