Silly question, but isn't the same amount of heat dissipated into the room with this mod? If you have a card cranking away at 150 watts what is the difference if that heat comes out of a radiator a few inches away? How useful is this if you have 20 cards hashing away in a room? I live in the deep south and I am trying to get my heat situation under control before the summer rolls back around.
Naturally, all that heat is still being dissipated into the room.
The difference is, with this mod you are able to dissipate greater amounts of heat much faster, thus keeping the cards at lower temperatures. With lower GPU core temps, you might be able to overclock the cards harder.
If you have 20 cards in a single room you better make sure your house AC is in tip-top condition before summer comes.
The water cooler also allows you to easily run a radiator outside.
Not those tiny ready-made CPU coolers. Those pumps are pathetically weak, just strong enough for a single radiator and two short hoses.
You could successfully build a decent WC-rig and mount the radiator outside but that's an expensive approach to cooling.