The setting files are in this folder: C:\Users\<user>\AppData\Local\Microsoft\MSBuild\v4.0

This is useful when your VS2010 import the include/library paths from earlier version of Visual Studio.

Reference: http://social.msdn.microsoft.com/Forums/en/vcgeneral/thread/dc9f28f0-4f56-4da2-8413-2116c10b31a6