Wow: to all you debating whether or not it actually took place are completely missing the point.
Some one said that it would be easy for someone to come up with that whole thing.... I beg to differ, it might seem easy enough because he did a really good job at making it understandable, however, to be able to create a sound argument for the meaning of life, the explanations to why we do what we do, even if it's a philosophical creation of his own is far from easy.
He gives explanations; he gives counter arguments and supplies satisfactory retorts. Everything works together to form the over arching theme, and he has worked in actual examples to explain things.
The explanations do not need to be true, it could be that none of what we know is actually how it is, but we'd rather have an idea of how something works and be wrong and not have any ideas at all. I think his piece provides a decent view of life, the universe, and god; even if it's not your thing, you can still say his idea is better than the old one, better than old religion.
I think it's safe to say that this piece is a think paper, not a guiding paper, the factuality of it is not as important as the readers ability to accept the what ifs he presents.