Lock-in by the back door
Ass soon as significant quantities of data start being pushed into this (or any cloud service) the situation becomes one of attrition. The costs of repatriating the data to your own facilities or even another cloud provider become prohibitive so the reality many of these deals are not perpetual. The chimps that sign then don't care because they will be long gone with a tidy bonus for "saving money" leaving, in this case, the tax payer screwed. With Amazon it will be screwed from every conceivable direction as they will be paying no tax on any of the profits they make from it.
