I'm missing a feature to add subtasks to a taks. Let's say I have Install Zimbra as a main task:

Install zimbra
-- install server
-- secure server
-- configure zimbra
-- deploy zimbra
-- test zimbra

It would be great to divide one larger task into several smaller one and sequentially mark parts of the task as done. If all subtasks would be done then the main task would be magically marked as done too!