I talk to people about programming with Virtual Earth quite often.  Beyond the developer APIs, my Virtual Earth knowledge somewhat limited.  I get asked all sorts of interesting questions about the technology behind Virtual Earth.  My answer is usually "Good question, I don’t know."  If you are one of those people that love know about all the nuts and bolts, then you are going to love Mark Brown’s new "Behind the Maps" series.   The first in the series covers the UltraCam.  Check it out here.