This is the elephant in the room and I'm surprised it hasn't been mentioned by any of the other comments.

When it comes to infrastructure as a service, it appears to me that there is an imbalance between the sensitivity of information entrusted to external systems on one hand, and the standards such systems are held up to on the other.

EDIT: case in point, on http://mongohq.com I can't find a single mention of the word "security". The language is all about ease of use, performance, scalability, disaster recovery, and low cost, but as far as I can tell not a single word is spent on what procedures are in place to safeguard your data from unwanted access.

EDIT: removed inflammatory comment.