Do you get annoyed by the warning:
If you are editing a group, and want to make a Duplicate of something, simply scroll to the item in the
Project Browser – right-click – Duplicate.
EDIT (added 5 Dec 2011):
In other words, this tip allows you to create a new Family Type in Edit Group mode. You may get annoyed when you aren’t allowed to make new Family Types when you are in Edit Group mode and Revit just keeps telling you:
Can’t create duplicates in Edit Group mode.
Just use the Project Browser instead – scroll down to the family in question, right click on a Type and Duplicate. Revit will let you do this, even while in Edit Group mode.