Running is the shit. I hate the indoor treadmill run though. I feel like a gerbil and get bored. I was running a lot last summer with a friend who was really good at pushing me, and we'd run at least six miles every other day. Having someone there to talk to and feed off of/distract you from the monotony of running is key for me. When I go out alone I don't ever go longer than two miles.
Cycling is where it's at though. Low impact, and I can really push myself to insanity. I used to live right on the river, which had a twenty mile trail that looped around both sides, and I would kill that in less than an hour every day...And then some asshole stole my bike.
Running in the winter is a chore. I'm a smoker, and the cold forces my lungs into overtime. By the end of a run I'm hacking up green shit and feel like dying.