CiviCooP is working with Emphanos on a nice CiviCRM project (of which I am sure Young-Jin will blog at some point in the near future). As part of this project I developed a specific extension that creates or updates Activity Types, Contact Types, Custom Groups with Custom Fields, Event Types, Groups, Membership Types, Option Groups with Option Values, Relationship Types and Tags from JSON files.
So for example there is a JSON file for activity types which looks like this: