Just installed and I love it!!! Check it out by clicking different styles at the bottom of the Admin menu on the sidebar. Just shows how powerful the whole CSS concept really is. Nice semantic XHTML markup with different stylesheets applied. Nice.
WP Style Switcher
This hack allows your visitors to change on the fly between CSS skins you make available. Installation instructions are in the README. You can see it in action in my Golf section. Latest release: Version 1.2, 2004-03-31.
The png-backs is the default style that is basically the style I developed for this site. It uses translucent .pngs to create a nice big-background image effect.