The main issue I have with all those services (this one, Parse, etc.) it that a large number of app require actual intelligence running on the server — in order to validate data, send emails, log some kind of analytics, trigger custom events, etc. The only service that I've seen so far which attempts something in that direction is StackMob, but they have severe limitations in other areas.

For example, when I was investigating backends services for Tehula, I initially thought I'd run with StackMob, but their HTML5 app model was a huge setback: they are geared towards single page apps, which means I couldn't do any routing on the server side. The only solution would have been to host an app somewhere else and use their REST api to talk to StackMob, which in the end I decided was far more complex than coding my own API.