Disclaimer- I only went from his responses to critics, in which some points weren't clear.
1: I just assumed (perhaps wrongly) that even Sam Harris would see the validity of an is-ought divide to some extent. If he hasn't, then I can refer to Hume and copy-paste his arguments for the win.
2: O.K then.
3: Refer to my disclaimer.
4: Which makes it even harder for him to go from an is to an ought, as he can't use the idea that he's merely following human intuitions somehow. He's following his own, very alien intuitions instead and can't justify them.
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?