I would say that their usefulness depends on how anal you are about corruption. By the rules of the game, all courthouses reduce corruption 50% and cost 1 coin maintenance. Remember that in Civ, round fractions down! So if you have 3 corruption, a courthouse will only reduce that to 2 corruption. So for me, the only reason to build a courthouse is if there is 4 or more corruption in a city. That way I make a profit: 4 corruption + courthouse = 2 corruption + 2 coins (at 100% tax). One coin pays for the courthouse each turn and the other is profit. If you have a corrupt government type (and in Civ there is no reason to have one after you build the Pyramids, usually in the BCs) and a single city is in a great location with multiple tile bonuses but is too far from your capital, then a courthouse is a good thing. I've started in Europe and built cities in south Africa and east Asia while still Despotism. If you aren't going to finish the Pyramids in the next few turns (or someone beat you to it on Emperor), that courthouse looks pretty good!