Well, there's at least one:

http://www.openstreetmap.org/index.html?mlat=50.813611&m...

http://en.wikipedia.org/wiki/Cerne_Abbas_giant

More seriously, there's "questionable" data in Google maps too like the fictitious town of Argleton:

http://en.wikipedia.org/wiki/Argleton

A geekier explanation of how it happened is here:

http://www.systemed.net/blog/legacy/131.html