I don't workout at the gym. At home while using my elliptical trainer I usually watch TV. I can great workout and watch a TV show or movie at the same time. Watching TV does make it a little harder to keep the pace up but frequently checking my speed and distance helps. So does limiting what I watch. Usually I workout while watching action TV shows or movies.
If I am not using an exercise machine I leave the TV off and just focus on the workout. I can't get myself to keep the intensity up while watching TV unless I have a lot of feedback, like a display telling me the speed, distance and calories burned.