The Patpong is no longer really the centre of this trade, as it has turned into a total tourist trap, complete with tacky market selling knocked off clothing and tourist tat.
There are still loads of live sex shows down there though. In fact you can't go further than about ten metres along the pavement without being grabbed by a tout who thrusts a menu in your face listing the activities that go on during the night at their bar (such as hookers putting razorblades in their vaginas, and shooting ping-pong balls out of them). I got hassled by them all the time, and I was walking along hand in hand with my girlfriend.
The area is worth going to just to see what it's like, but the sight of all of these prostitutes lined up outside the clubs in evening gowns, with numbers on their chests like they were on a menu reminded me of some sick and twisted takeaway.