I just released GoogleMap Control 4.1 beta.
Get it from codeplex, and give it a try.

Release Notes

In this release were fixed some important issues like: large number of markers using geocoding, zoom end event cycling etc.
Some new features were implemented as well, check out the list below.
I would like to highlight the proper implementation of Marker Manager coming in this release.
Check out the list of changes connected with that feature below.

Issues

• Large number of markers using geocoding
  • Issue with creating large number of Markers
  • Subsequent markers don't show after unsuccessful geocode
  • Random missing markers when using address property and adding more than 10?
• ZoomEnd event subscribing problems
  • OnZoomEnd issue

Features

• MarkerManager - MarkerManager is used to manage visibility of hundreds of markers on a map, based on the map's current viewport and zoom level.
  • The GoogleMaps API GMarkerManager class is deprecated and I have used the recommended open sourced MarkerManager instead.
  • I have added a new inner property MarkerManagerOptions in order to manager the options for the marker manager.
  • GoogleMarker class was changed and couple of new properties were added to it to: MaxZoom and MinZoom.
  • A sample page was added to Samples Website under /marker/MarkerManager.aspx. Check the sample page online here
  • Check out the short demo video (coming soon)
• Map
  • Enterprise / Premier support
• Directions
  • Add 'preserveViewport' functionality
• Polygon
  • Polygon EnableDrawing & EnableEditing

Changes

• The Anonymous JS classes' functions were changed to Pseudo-Named functions for better JS debug and error feedback experience.
• Samples Websites for .NET 2.0 and VB were removed - Sorry, guys, I just have no enough time to support and keep them up to date.

Regards