The way I see it, I won't ever trust someone else's verification system to be accurate enough that I would be willing to lock people out of using my software.
I see where you're coming from, but I suggest having MS worry about Windows validation.
In addition, there's really no way to know the true legal status of an install through the machine itself. Sure, there's "validation" and all that jazz, but that's nigh meaningless in context of the truth.
