Google just released support for KML overlays via their API.  Google Maps has supported the overlay of KMLfor a while, but I have been waiting for API support since Fall of last year.  I am using this for a project with BayAccess, a non-profit promoting safe a clean recreational use of the the San Francisco bay.

Before: http://www.danharrelson.com/bayaccess/iframe.html

After: http://www.danharrelson.com/bayaccess/index.html (need to add in the other KML feeds)

I tried to build a page pulling in a KML for one of my bike rides, but of course I pick a time when MotionBased having trouble so the feed is intermittent so I saved the KML to my site.  IE won’t display this properly either, so use FireFox. 
http://www.danharrelson.com/t/bike.html
 
Google Maps renders it, but tells you that there’s an error in the KML: 
http://maps.google.com/maps?q=http://www.danharrelson.com/t/MotionBasedExport.kml

Update: Chris contacted his collegue at Google who implemented the KML overlay feature and I was pointed to the documentation which outlines the proper way to write a page.  The bike map is corrected now and works on IE.