Current functionality supports duplicating tasks in projects but not in project templates. This would improve user experience when building tasks in project templates, since many are worthy of getting copied.
You can actually do this via the "Copy To" functionality--you just copy to the same template you are in. The steps in the process are cumbersome, however, so it would be easier and more consistent/intuitive if the functionality were the same between Projects and Templates.
To Kristen: Yes, we're aware of the "Copy To" functionality. My suggestion is to have the same "Duplicate Task" functionality that exists in the Project objects, because of its ease-of-use and quickness.