In the HG repository, there are so many Visual Studio solutions and projects.
I think there should only be one solution for Visual Studio 2010. Maybe another for Visual Studio 2012.
Understanding MSBuild with its targets and prefs can help us build new configurations, such as, Window8UI, Mono, MonoOnAndroid, Silverlight, and General.
I noticed this is how the Gstreamer SDK at
http://www.gstreamer.com/ has handled their solution/projects in Visual Studio 2010. There was a configuration for 32-bit and a configuration for 64-bit. Each configuration pointed to different targets/prefs. These prefs files set the varous defines and compiler switches.