I don't have the book, so I don't think I'm eligible for the prize. Suffice to say that I've read his summary on "Response to Critics", and anybody who can't refute the tripe philosophy shown there (maybe he's got better in the book, I can't be sure) doesn't deserve to be considered anything more than a crap philosopher.
I have read the book, and consider it tripe all the way down. I've "discussed" it with others at his project-reason site as well. None of his supporters can make a coherent case out of what he said.
Sam Harris is here offering a substantial amount of money to anyone who can show a flaw in the philosophy of 'The Moral Landscape' in 1000 word or less, or at least the best attempt.
http://www.samharris.org/blog/item/the-moral-landscape-challenge1
Up to $20,000 is on offer, although that's only if you change his mind. Whilst we know that this is very difficult, note how few people offer large sums of money for the privelage of being disproven.
In case anyone does win, I will remind you that this site is created and maintained by people who work at MIRI and CFAR, which rely on outside donations, and with whom I am not affiliated.
Note: Is this misplaced in Discussion? I imagine that it could be easily overlooked in an open thread by the sorts of people who would be able to use this information well?