Although there would be no way to actual prove it, I believe that somewhere in the United States someone is watching an episode of The Simpsons or Star Trek every minute of a 24 hour day.
Why? Well, both shows have been released on DVD. With Star Trek, I"ll limiit it to Star Trek Original Series and Star Trek Next Generation, but there are 10 DVD sets of those shows as well as 11 series of the Simpsons.
Both shows are also heavily syndicated. People are either watching syndicated episodes as they air or on Tivo.
Both shows have fans who watch episodes over and over. Even for the casual fan, both series hold up fairly well to repeated viewing.
Any other shows which are like this?