For those who tried installing the Bing Maps App SDK (http://connect.microsoft.com/bingmapapps) you will likely come upon the following error when running the .msi.
Even though I had Visual Studio 2010 (Premium) installed and the latest Silverlight 4.0 runtime installed, I still received the error. Unfortunately I tried every combination of installing/un-installing all variations of the Silverlight Tools 4 for VS 2010 to no avail. The solution is strangely tied to a specific version of the SL 4 tools and specific SL runtime with that build, and must be followed as below:
1) Un-install all instances of the SL runtime, SL SDK, and SL Tools for VS 2010
2) Download and install the SL Tools (beta) for VS 2010 build here: http://go.microsoft.com/fwlink/?LinkId=177508
3) Run BingMapAppSDK.msi
If the steps above were followed correctly, you should move onto the next screen.