I went to the first Google Drive developer meeting at the Googleplex. The API and SDK are at https://developers.google.com/drive
I really didn't quite understand what the difference was between the old Google Documents and Google Drive. The main difference is that all of the other Google services and their own APIs could only work on with the extension types that they know how to handle.
Google Drive lets the application developer work with any type of data that is on Google Drive or referenced. They consider Google Drive as user managed content as opposed to an application developer who manages the content.
There was a couple of demos of a wireframe app. and an app that would work with an Autocad file.
They currently support Java, PHP, Ruby, .net and some other languages and plan to support more.
The Google Drive applications can work with any browser. These Google Drive apps are gotten from the Chrome App store and they are the only apps that will work with other browsers.
Somebody asked about working with info when offline. The presenter said it is up to the App developer.
Ideally what I would like to see is to store programs on the Google Drive and then run them from an app. In that way you could use a Chromebook to do development.
I realize that a lot of this stuff can be done through other web sites but Google Drive is designed to be a general purpose storage area controlled by the user.