The .xxx domain might be successful if it can gain a reputation for only allowing "reputable" porn sites that don't engage in deceptive or fraudulent practices. If it can establish a brand name then it might be able to drive the junk porn sites off the net as their business dries up. Otherwise, all its not going to be of much use except as a way to part porn site operators of registration fees.
That's an interesting idea. People would pay for quality, so those which are amature sites that want to receive some form of payment for their material would push to gain access to that domain, moving more off the .com sites. It would be interesting to see if that worked.
Speaking of which, how is the .tv series working? I don't hear people advertising that any more.