Thanks to the relatively open structure of Google Earth, a Wikipedian named Stefan Kühn was able to provide a set of Google KML files for about a year or so which was widely used:

http://www.webkuehn.de/hobbys/wikipedia/geokoordinaten/index_en.htm

Ooohh this IS cool! I <3 Wikipedia :P

I just tried to overlay Stefan's file on Google Maps (both as KMZ, and unzipped as KML), but it seems to be too big. Google Maps just says, "File not found at ...".

Philipp: Yes, this is documented. Maybe it will be fixed in the future.

Philip

There is a wikipedia – google maps mashup over at geonames.org :
http://www.geonames.org/maps/wikipedia.html

There are over 500.000 articles in 210 languages extracted from wikipedia. The balloon shows an excerpt from the article.
http://www.geonames.org/wikipedia.html

The mashup also displays semantic information like population or feature type.