OK, I've built a reflector that ties KML to existing WMS servers. Its not as nice as haveing GE read capabilities docments directly but it does give us instant access to a LOT more data.

Feel free to add the following URL as a network link. (For best results set view-based refresh to after camera stops)

I can't say that it will remain up forever, especialy if it gets hit a lot!
Also, I'm open to requests for specific WMSs as it is easy to add them just let me now.

http://www.geovista.psu.edu/kml/kml2wms.jsp