to answer your mile/2mile question, yes.
i trained a lot on a treadmill my senior year of college due to my job as an intern. i often got home too late during the winter months, and could not run in the dark where i went to school. so, i trained at home on a treadmill those nights. i still managed to put myself in awsome shape, running 65 hard minutes per night (at least 10.5 miles) and mixing in a few morning runs outside. of course i also did my indoor track workouts to keep speed.
i managed to drop my mile from 4:21 to 4:13 and my 3000 from 8:55 to 8:39, running it only once. (not amazing times, i admit, but decent improvements)
i'm not gonna lie and say the treadmill played the only roll in that. i ran hard workouts and great mileage all winter (70-80 miles each week).
obviously there's no true substitute for running outside. but i find the treadmill, for me personally, to provide an excellent workout.
use it especially when footing is bad, or darkness, like myself.