If you come across J2ee portals you will realize, that they use skins to make the look and feel uniform. I worked with Websphere portal and found, that I only could use the skins though JSP. Since I like XSLT driven UIs better I started this little servlet to make the process very transparent.
In your html you have a request like /resources/assets/logo.jpg (e.g. in your image tag). The servlet will add the browser type, the browser language and a skin (from a cookie for now). It then seraches for the asset and returns the best match.
... more doku to come
If you want to see what you can do whith skins visit CSS Zengarden. It is all in the skins.