I have a 20 gallon set up under my wall-mounted tv. I built a stand for the tank and to hold the DVR, xBox, DVD player, cable modem and router underneath it. So far I don't mind the lights though if we were going to watch a movie I would probably turn them out.
I have a 55 and a 29 under a 42" plasma. I recommend covers on the tank so moisture from evap doesn't get into the electronic components in the tv. I have had the tanks under the tv for 5 months with no problems.