This is a pretty thorough article for example :
http://www.marketwatch.com/news/story/lo...93F0C66A1B2E%7D
The basic problem to me is there are so many people high on Amazon and so many large funds holding it that it may not correct down until some really bad news comes out. I personally believe this is a huge over-valuation, and that the US consumer market which drives Amazon is going to get very weak in the next few years as the subprime market pinches spending power and people don't have all those refis to boost their capital.