It is obvious just from having lived in Seattle for a good long while that something is up with Amazon. They are notorious for employee churn, and it's easy to see this in my circle of acquaintances, many if not most of whom work in software. People do quit Microsoft, Google, or Facebook from time to time, but it's generally a long-term engagement; Amazon is a place where even relatively senior people don't seem to stick around more than a couple of years.
It's not a scientific study but I don't need scientific accuracy in order to get a pretty clear idea where I would or would not want to work.
