I was first alerted to the Manhattan Declaration by my friend Paul. Whatever else you want to say about it this much is sure: opinions are forming fast. John Stackhouse says it is a waste of time. My friend Paul and Kevin DeYoung are encouraging people to at least read it if not also sign it. Jeff at Scripture Zealot has put together a few links with varying viewpoints which I found helpful.
Stackhouse complains that the document does not indicate what anyone is supposed to do besides sign it and he says "the document seems philosophically and politically incoherent." With opinions this strong I want to take a little more time with it but won't have that luxury till after Thanksgiving.
On another note if you've not read Kevin DeYoung's post on The Gospel Old and New I would encourage you to read it. It's very good (and there's nothing to sign).