Microsoft's Virtual Earth is the competitor of Google Earth. Not much has been said about Virtual Earth. It simply comprises of similar features to that of Google Earth in terms of navigation however, Google Earth is just too ahead of Virtual Earth in terms of usage and its various features such as importing sketchup models and creating your own mashups. New features are still getting developed for Google Earth users. I guess one of the cool feature of Virtual Earth is navigating via a browser which shows 3D buildings as well and the quality of the resolution of the 3D buildings is much better than Google Earth.However, a plugin needs to be downloaded which can take several minutes.
Below is a video showing Stephen Lawler of Microsoft giving a talk on Virtual Earth.
Below is a video showing Virtual Earth in action:
More info visit: Inside Microsoft blog post.