Zoom level based grouping (or based on distance). The problem is: I display a world map with all items, and now adds all photos too, but user can't distinguish between photos because they are so close. Grouped items could be displayed with bigger markers. Like a tagcloud, but for images/albums in a region. Maybe this feature already exists, but grouping doesn't work for me, I've submitted a bug.
The Markers Settings page has an option for Automatic Item Regroup which will probably do what you want. However, it's suboptimal and needs to be revised. The MarkerManager function from the gmaps-utility-library could be helpful.