Taking a look at the 2 year IV30TM chart for AMZN we can easily see how it tends to spike near earnings and then drop off. See the image below from the Livevol Charts Tab (click the image to enlarge).
This behavior is not that uncommon. Earnings represents a known news event that could affect the stock price more than average; that single day therefore should have a substantially higher expected volatility. This phenomenon is referred to as "earnings vol" by most professional traders.
What's more interesting about AMZN is how low it's volatility has gone recently. The images below are available by holding the left mouse button down on the vol chart in the Charts Tab.
The 2 year low in IV30TM for AMZN has been 36 (on 5/16/2008). As of 9/18/2009 the IV30TM hit 37. Since hitting that virtual support in vol (I drew in a yellow line illustrating the vol support in the image below), AMZN IV30TM has begun to diverge from that low. See the image below (again, you can click the image to enlarge it; the red line is IV30TM, the blue HV30TM).
With AMZN earnings coming on or around 10/22/2009 and its tendency to demonstrate strong earnings vol, together with the fact that it has reached and bounced off of a 2 year volatility low, maybe this is just the beginning of a run up in AMZN volatility. It makes me wonder if maybe, "Here comes the vol"?