Well, a useless thing will be the cost of the fiasco in the Middle East if costs continue for the next several years. Already we've reached half that amount and have nothing to show for it other than thousands of families who have lost their sons, tens of thousands critically wounded, and more terrorist acts than at any point in history.
Bloomberg.com: Opinion
What useful things could be done with $1 trillion?
We could wipe out malaria in Africa...and still have hundreds of billions left over.
5 million new homes for Americans (imagine the economic growth this would cause).
We could replace 50,000,000 old cars with newer ones that consume less gasoline and pollute less.
Any others?