Are you an Apple Developer? The only ones I know who have Mountain Lion (beta) are Apple Developers. It is my understanding that If an Apple Developer gave you a copy and Apple found out, they would not be pleased with the action Apple would take.
Not an "Apple developer". We have a side business that develops proprietary apps for businesses. Apps made to order for companies and apps that companies may choose to release under their own name. Both iOS apps and OSX applications. We have developer licenses with several manufacturers.
Lest you think smoke is being blown. This is from my older MacBook Pro. We have many different Macs out in the office.