1.5 year after my first (failed) short experience, I shorted 200 shares of AMZN today @ $32.87. I feel the market overall is running risk and want to exploit it by shorting.
With average annual earning estimate of $0.63, the stock is trading at 53x P/E. With 2002 annual revenue of $3.9b, I don't think the company can sustain a 30% growth rate. Room of profit margin improvement seems to be quite limited as I noticed smaller specialty online retailers can beat Amazon price most of the case. (I might have a bias evaluating this because I live in Washington and need to pay sales tax for purchasing from Amazon.com.) Also, Amazon has not turned sustained positive FCF. The excessive new issurance (due to stock option plan) is also a concern for earning dilution.
(I've also considered shorting EBAY and YHOO, which I believed are overvalued too. However, unlike Amazon.com, both have substantial earnings and positive cash flows.)