I had also experimented with Virtual Earth a while ago.  What I wanted to do was use Google Earth to easily place/name/link certain points on a map, and then use Virtual Earth to display them.  When I tried this (Virtual Earth version 5 I think), there was no support for KML.  Then I saw this: http://blogs.msdn.com/publicsector/archive/2007/12/27/virtual-earth-map-control-now-supports-kml.aspx .  Very cool.  Good for interoperability, good for development, good for me.  I now have a project in mind - mapping bike trails, hikes, and geocaches using Virtual Earth, my GPS, Google Earth to create the KML files easily - all easily available on the web.