You just have to check this out. Ricky Brundritt has created a Flight Simulator for Virtual Earth by writing a plug-in for the VE3D MapControl. In his 4 part blog series he also explains the making of and provides the source code. The control even leverages the local time. Ricky, this is just great!!!
The 3D control is usually started through the Virtual Earth AJAX MapControl but there is also a documented SDK that allows you to access the assemblies directly and extend them with your own plug-ins. On their blog the VE3D team provides lots of helpful information and sample applications to get you started.
The VE3D API is one of now 5 documented APIs for Virtual Earth but before you get carried away keep in mind that only 2 of these APIs are officially supported: the AJAX and the SOAP API. The VE3D API is still a beta and the Silverlight API is a Community Technology Preview (CTP). The ASP.NET Server Control is part of the Windows Live Tools for Visual Studio and a CTP as well. It is basically a wrapper around the AJAX control.