Wow, such a jerk. If we had been all notified Parallels 6 was dead on arrival in Mountain Lion, such as an e-mail since I'm registered, we would have postponed the update. As it stands, Parallels took the "screw you and hold you hostage" approach charging $50 following a $20 OS upgrade. And they don't apologize or care. Get the facts.
Parallels seems to have no problem pushing out unrelated advertisements to paid users, but important details such as this, no mention was made.