Datastore vs spreadsheet for provisioning Google apps
If you use the Datastore API, you will also need to build out a way to manage users data in the system.
If you use Spreadsheets, that will serve as your way to manage users data, so in that way managing the data would be taken care of for you.
The benefits to use the Datastore API would be if you'd like to have a seamless integration of managing the user data into your application.  Spreadsheet integration would remain separate from your main application.
In my company we want to build an application in Google app engine which will manage user provisioning to Google apps. But we do not really know what data source to use?
We made two propositions :

spreadsheet which will contains users' data and we will use spreadsheet API to get this data and use it for user provisioning
Datastore which will contains also users' data and this time we will use Datastore API.

Please note that my company has 3493 users and we do not know too many advantages and disadvantages of each solution.
Any suggestions please?