Apart from the scams involving people interested in "learning english," I would like to warn you all of something potentially a lot more dangerous. I was in the bar area of Sanlitun, which has a lot of beer bars etc. I kept getting approached by people offering "girls, cheap price, 100RMB" etc. At first I just said no but eventually curiosity got the better of me. So I went with a lady in a taxi to a place called Beijing Liu Hotel. I checked the price and they confirmed 100RMB for the girl. So I chose a very pretty young girl and we went into a small private room with a couch and KTV equipment.
Basically, within 5 minutes they had brought in a plate of food which I said I didn't want. So the girl talked to them in Chinese and the result was that they brought in more food and drink. I could see this was a scam so I went to pay, and the bill came to 700RMB (for 10 minutes in the room just talking to a girl). I tried to refuse to pay for the whisky (which I hadn't ordered), at which point the manager and several goons grabbed hold of me and dragged me into a side room. Obviously, at this point I had no choice but to pay. After leaving, I went straight to the police to tell them I had been robbed but they weren't interested. They sent me to another police station which at that time of night I couldn't find as taxi driver's in Beijing don't speak English.
So basically, I would warn you not to go with anyone that speaks English and tries to take you to a massage parlour, offers "girls", KTV, etc. They will give you a huge bill and probably beat you up and steal your money if you don't pay. The police in China really don't care either. If you are determined to find some action in China you need to find the place yourself. The barbershops seem to be safe enough and generally you won't get scammed there, although they don't speak any English. It's probably best that, wherever you go, you only carry as much as you intend to spend (and no credit cards) and that you tell them just how little money you have when you arrive.