Organic Groups comes with a "Group default list" field formatter out of the box. This module was created to add extra formatters for the Groups Audience field.
The first formatter that is added in this project is the "Group delimited list" formatter which allows you to display Group names (labels) as a delimited list. The taxonomy_formatter module was used as an example for this formatter since it does exactly the same thing for taxonomy terms.
If any additional formatters are required please let me know trough the issue queue.
This module currently only works with the 7.x-1.x version of Organic Groups.
In OG 7.x-2.x the Group field has been replaced by the entityreference field.
Development of this module is sponsored by LimoenGroen, Amsterdam-based Drupal specialists.