I've never posted a review on Amazon, but I'm always surprised at how well they all seem to be written and not at all spoilery. Or at least, where there are spoilers, they are clearly stated as being present beforehand. Also, I've never heard of the reviewers dissing each other or starting flame wars. I figure there are guidelines you're supposed to follow when posting a review, and people abide by them. I can't imagine somebody at Amazon screening all the reviews before they are published - you'd need a whole planet of somebodys for that.
I guess that's how reviews like these are even possible. I especially liked number four.