AppVerifier is a cool tool to test your applications in places where you could have missed them. Basically, you can read more about it http://technet.microsoft.com/en-us/library/bb457063.aspx
For example: I was able to catch an error in my application where I was trying to release a variable which was already released. Even though this was compiling fine, and running correctly, it was throwing an error when I checked it with AppVerifier because of Heap error.