Currently, Google's base imagery and custom base map types have a smooth zooming transition effect where the old tiles are stretched/shrunk while the new tiles are being loaded.

Adding overlay map types on top of Google's imagery, however, does not have this smooth transition: those images instead "flicker" while zooming, since the images are unloaded while the base imagery behind it is smoothly transitioned, then the new zoom level is loaded.

Example: http://www.hbs.edu/maps/. Try zooming in and out a few times.

Having the same transition effect for overlay map types would provide a much smoother user experience.

Thanks,
Allan, concept3d Inc.