None of us really knew for sure if Diane was real until we saw her. I think it's great that she's a real person. However, I think they missed a trick here. What if Diane had turned out to be a man? This could have been a transvestite like Denise, or it could have just been a regular dude called Dave or whatever and the whole "Diane" thing could have just been a joke between him and Dale. It could have been Dale's way of poking fun at him for having (what is traditionally considered) a woman's job. But maybe the joke could wear thin after a while. I imagine Dave sat there transcribing the thousandth tape from Cooper and letting out a big sigh and saying, "Yeah yeah yeah, here we go with the Diane thing yet again..."