This is one application I have developed for WP7. It is a map of the night sky and at the same time a three dimensional map of the nearest stars. You can switch between a view from the Earth and a Space view of the nearest stars. A 3D view of the solar system is coming soon. This is a link to the Windows Phone Marketplace: http://social.zune.net/redirect?type=phoneApp&id=960d8167-c43c-e011-854c-00237de2db9e

The website for the project is http://www.stars-3d.com/

A short introductory video can be found on YouTube at http://www.youtube.com/watch?v=UmdW6rH2K0o and also another one at http://www.youtube.com/watch?v=0pCtfvLPLZw

I use XNA as a platform for this project. It is quite mature framework for working with 3D world. The system uses device GPS when drawing the local horizon and stars visible from a viewers specific location.

I am waiting for Microsoft to release the Compass API so I can implement the point to sky feature and the app will scroll to the portion of the sky you are pointing to.