GIS (and .NET) pro Brian Flood weighs in with assessment of Google Earth as an Enterprise GIS client.
Brian is most enthusiastic about the network link:
This one feature opens the door to an enormous amount of real time customization and will probably push GE as the de facto standard for 3D visualization over the internet.
He also points to some limitations the free client has vs. the pro version when it comes to streaming vectors from servers. Finally, he seems to have built a pretty robust KML and WMS server for Google Earth, which is promising, considering that he blogs at a company that specializes in GIS solutions for municipalities.