Some of it may be the new colored icons. I'm not quite sure where the icon images are served from. I suspect they are coming to you from comcast instead of google. That is one factor.
Also I recently doubled the number of pins in an attempt to make the pins show properly when the map is zoomed to a world view. When the date line shows and it is just a bit too far right, all the pins disappear. They arn't gone, just off the page to the right on the next panel of the map. I'm still looking for alternate (faster) solutions.
If the map is zoomed out far enough you see multiple panels, divided at the dateline. By defualt, Google only puts markers on one panel, the one that holds the center of the map window. When the date line scrolls past the middle of the window all the markers jump to that panel.
If any wish to see what the map looks like without the doubleing of pins look at
http://home.comcast.net/~gkbeer/ssr/pinmap/index2.htm
In that version of the map scroll the US over to the far right side and back.
