[peterwwillis]

When they mention companies using DynamoDB, at least one of those actually uses their own implementation of Dynamo that they wrote to work around cost and performance limitations.

The main problems faced are not the ability to scale or reach performance benchmarks or keep data safe. They are operational, and primarily problems of infrastructure complexity and management. Oh, and having developers architect and manage the operations of a really freaking huge service is a bad idea. (No offense intended - those developers don't want to be woken up in the middle of the night either)