(Richard Grevers dramatic@xtra.co.nz): How does the user preferences table stores the user's preferred stylesheet? Is it just an index number, or does it contain the URI for the stylesheet? If the latter, may I suggest that we allow users to specify the location of a personal style sheet for wikipedia. For example, I could then take the Cologne blue stylesheet, change the things I don't like about it (such as the article text size) and host it on my own webserver*, point to it from my wkipedia preferences, et voila - a fully customized view of wikipedia, but I am actually reducing the load on the wikipedia.org servers by not getting a stylesheet from them.
Preferences only stores the index number of your skin, which indexes the standard stylesheet of that skin. If you want to tweak the styles, you should be able to do that with your browser, telling it to override whatever the wikipedia stylesheet says.