My response (posted below) basically gives some pointers for what other people (often creating custom implementations of Google Maps on their sites) are doing to avoid the problem of 'decluttering' or 'declustering' multiple points at the same location (same coordinates). My question is: how do you handle declustering on your Drupal site? Are there any perferred techniques? Luckily for me, this is a problem I have yet to encounter, as I've only had to map locations of stores, parishes, etc., that are already spread out evenly over some area of a map :-)
My response to his question follows:
With regard to your question about making a map more usable when there are multiple markers on one specific geolocation (same latitude and longitude):
I know that there's one thing that the Mapstraction module does, called 'declutter points', that might be able to help. I've also found some good hints when looking up clustering and Google Maps on Google search.