I had a boyfriend about 13 years ago who had this, it was a nightmare.
He could have sex, and it went on for ages and ages but could just not ejaculate so everything sort of ended in a bit of a flop as you might imagine. You might think that a man going on for hours might be great for the woman but it really wasn't. It was very sore actually and really remarkably dull and passionless. He wouldn't masturbate in front of me either.
I found it incredibly frustrating - intially I wanted to love him and try and help him (oh the innocence of youth!) so I put up with it.
We decided to stop using condoms after a while (I was on the pill) and then it all became worse. He said he loved me and wanted to be with me and it was just a physical problem. I beleived him for a while.
Eventually I said to him that I couldn't continue like this. he admitted that at the age of 16 he had had sex on a beach (his first time - with a woman he didn't know) and it then became apparent to me that he was actually almost obsessively anxious about HIV (later turned out he had been having almost weekly HIV tests during our 2 year relationship). So he went for counselling with relate to try and help his anxiety - he went on his own, didn't want me to go.
The shortly after I found evidence of him in our bed with another woman - clearly having had an orgasm. So that was the end of that!
Hope your experience is better than mine...
Actually I think the guy I am talking about is fortunatly not representative of men with this problem. He was completely screwed up on many levels, and probably in retrospect had OCD and a form of mental illnes causing his obsession with the risk of infection.
Sorry if this sounds very negative about men with this condition, it is not meant to be!