The new user can be added to the project or task and data already entered is preserved. This is done by removing the form's default save action and implementing actions for each and every submit button. The submit button will dump the data into the params map and all that is required is to store/forward it along then retrieve it back afterwards.
The new user is to be notified by an email containing a link back to the project/task. The messagingService is responsible for this but has not yet been created.
More information here :)