For our final project in 6.813 (User Interface Design & Implementation), Nick Joliat and I designed a "geographic wiki" application. I have posted a Flash-based prototype/demo, but please note that it is intended only to illustrate the basic structure of the application! I had hoped to develop a full-featured HTML version by the end of summer 2010, but you know how these things go.
Map Wikipedia Category
To tangentially make up for your disappointment, here's a bookmarklet I made to map the pages in a Wikipedia category: Map Wikipedia Category. Right-click that link and "Bookmark". Then, when you are on a Wikipedia category page, select the bookmark. You will get an output like this, assuming you happen to be interested in bridges in California. (This bookmarklet uses toolserver.org's kmlexport service.)