Thought people here might find this tiny library useful. It makes
overlapping map markers in the v3 API behave like they do in Google
Earth, springing apart when clicked, so the user can choose one.
More details here:
http://blog.mackerron.com/2011/06/overlapping-marker-spiderfier/
Note that this is related but not the same as clustering -- notably,
clustering won't help you when your markers still overlap even at
maximum zoom.