We're currently on DynamoDB, and it has given us some real headaches, so I wish these guys luck! Amazon iterates quickly (well, quickly for a megacorp) so we're still hopeful about seeing improvements.
Yeah, I've considered that before. Thanks for the suggestion. If you want me to ping you when I get around to writing it, drop me an email (address is in my profile).
Here's a good explanation from a MongoHQ founder about why you should choose them over DynamoDB: http://stackoverflow.com/questions/11741977/choosing-a-datab...