How about a task template per say. Many of us have tasks that recur that have subtasks.. For example, in IT, when a new employee starts, we may have to provision his login, e-mail, assign him a phone and voice mail, configure a security key card for building access, order/configure equipment, etc. Having a task template for new employee, that has all of these subtasks predefined would be fantastic. That way you don't have to manually create all of the subtasks each time.
Also if you receive a task from someone, is it possible for you to create your own subtasks on it?