re: GIS in MediaWiki.
With $wgRawHthml = true, the following HTML puts a map in a wiki article.
<div style="float: right"> <iframe src="http://openlayers.org/viewer/?toolbar=1" width="400px" height="400px" scrolling="no" marginwidth="0" marginheight="0" frameborder="0"> </iframe> </div>
What modifications might make wikipedia.org comfortable with the security of this type of iframe? The whitelist feature in MediaWiki might be extended to allow particular domain names in the src attribute.
OpenLayers is a young open source project. Upcoming releases will make it easy to put markers in the maps and to use more backdrop mapserver accessible on the 'net --- currently it can load WMS and WFS layers.
John