I run on a treadmill for about half my weekly runs. I find running on a treadmill harder than running outside, but my DH finds exactly the opposite. I find listening to music helps to pass the time better than watching TV. It is very hard not to keep looking at the clock though. But, I'm not willing to run alone at night when it's dark out (I run in a city park) and I can't run during the day except at the gym, so I save my outdoor runs for the weekend.