I sometimes look at my list of Twitter followers to see where they are geographically but this involves looking at their entries one by one. Mapmyfollowers allows one to use a mashup developed by Scotia Systems . ReadWriteWeb says "that allows you to see where in the world the people who follow you on Twitter are. Up to 1000 at a time can be viewed on a map and there's something magical about the resulting experience."
I logged into MapMyFollowers and, after giving them access to my Twitter account, was able to produce a map within a minute or two.
|Geniaus' Followers on Twitter|