Change.org (which Amazon supposedly hosts) claims it's due to a Chinese attack (this from an email I received):
Here's how we know it's really gotten Beijing’s attention: For the past four days, the Change.org website has been repeatedly targeted by cyber attacks coming from China that aim to bring our site down, which would keep people from signing the petition.
Here's how we know it's really gotten Beijing’s attention: For the past four days, the Change.org website has been repeatedly targeted by cyber attacks coming from China that aim to bring our site down, which would keep people from signing the petition.