The guys above have good suggestions and the advise is the safest / cleanest way to go.
What I have done is run my cable (lifeline service) directly to the TVs in the house. My rooftop antenna is split and run to the tuner and the HDTV STB / Satellite receiver. The cable for the one room that I have satellite, I have the cable going to the diplexer and the TV, to where it gets mixed with the satellite signal and then to the STB. My purist side hates mixing signals and running them together to a box, but the my wife thinks it is rediculous to switch between 2 inputs on the TV set when all can be done from the STB. It all works decently together, and the unmixed signal to the TV looks almost identical to the diplexed signal.
As I get additional satellite boxes, I will probably use the diplexed signal, because my wiring is installed in the walls. I know another guy that is doing this as well and it seems to work OK... The guy next door just had a satellite installed and the installers ran the wire on the exterior of his house...
The other thing to consider is to make sure that the cable installed is RG-6 and not RG-59. The RG-6 has better shielding, and is recommended for all AV installations.
With all of the home networking available, it can't hurt to have the extra runs.