Never heard him? Not to derive this into some "list of Paul Graham's speaks", but I really suggest to watch http://www.youtube.com/watch?v=q7K0vRUKXKc. A good speak, I think.
It freaked me out when I found out pg spoke with an American accent. I just assumed he had an English one from his place of birth. D'oh!
I heard him speak first and then ended up reading all his essays, hearing them in his voice.
I've read some of what he's written - I thought he came across as much more "normal" in that video. It improved my opinion of him considerably...
Funny, I always thought Paul would speak in received pronunciation... :-)