The instability/unreliability of the Drive API can't be understated. I used to have almost my entire app rely heavily on gdocs, but the api is far too shaky. Even wrapping every API call in a try_5_times function (which would often take 2-3 requests before getting a non-500), server errors would get through. Critical components of the API would go down for hours -- once, the entire day -- sometimes without even a blip on the status page.

While the api is a little funny, it's clearly very powerful. Anyone criticizing the move to work with Google API's at all should keep that in mind. But the nonexistent service and unreliability of the API are hard to overcome.