O'Grady on DynamoDB
Great analysis, as usual, from Stephen O'Grady of Redmonk. Here's the part about Dynamo that concerns me, the lock-in:
Amazon DynamoDB: First Look: Like the initial wave of PaaS platforms, however, DynamoDB is available only through a single provider. Unlike Amazons RDS, which is essentially compatible with MySQL, DynamoDB users will be unable to migrate off of the service seamlessly. The featureset can be replicated using externally available code via those projects that were originally inspired by DynamoDB, for example but you cannot at this time download, install and run DynamoDB locally.