After introducing the timeline for user profiles, Facebook is now archiving groups created using the old format and migrating them to the new design.
The users who are in the groups that were created using the old format will see the message on their home pages.
What happens to the old groups then? Here’s the screen shot of the post available on Facebook Help
Its not yet clear what actually are the groups created using the old group or groups created before which date are the old groups?