The OLPC community is currently using a custom map mashup to help volunteers and school projects around the world find one another.[1] It's not hard to skin. http://olpcmap.net http://code.google.com/p/olpc-map-net/
There was recently a discussion about using this tool on the cultural-partnerships list. Are there existing collaborative maps of Wikimedia groups and projects? Is this something worth trying?
SJ
[1] For OLPC this provided a happy medium between mapping "all users" and mapping "large established regional groups", neither of which captured the energy of the small innovative projects which drove and defined local communities. More detail: http://blogs.law.harvard.edu/sj/2011/01/27/mapping-global-communities/