For all its mind-sucking boredom, there is actually some good about treadmills that I had forgotten:
Climate control. It's still 90 degrees and 80% humidity as I type this at 10:30pm. The gym is always low 70s and lower humidity. It's always light, no heat of the day, no thunderstorms.
Predictability. I know exactly what's coming (nothing). No dogs, no squirrels to dodge, no bikers sharing the sidewalk, I don't have to lug around my mace.
Elevation. I run in the flattest city in the state, yet Chicago has that nice incline at the 26th mile. I can now train for that.
Tempo. It's a lot easier to push the tempo when the machine is doing it and my only job is to keep up.
Cubbies for my keys (and a sweat towel or water if I want it).
Besides, it never hurts to break it up with an episode of Jeopardy! mid-run :) I'm going to get my $$ worth this month!