This is an interesting question, and one I am not sure I can shed any light on either. I am sure it has a lot to do with the intention behind the pain.

I am not into pain, but know that the few times my Master has asked me to do something that went beyond my normal pain threashold, I have done it. Unlike some I get no rush out of the pain, but there is a certain sense of achievment in doing something I didn't think I could do.

So I am not sure if I find the pain erotic, but I do find it erotic to push myself that bit more for my Master.

I will be interested in other responses too.