I mostly find running exciting because of the changing scenery, people around me and freedom to set my own pace / terrain. I also find the repetitive action of treadmills leads to discomfort and ultimately niggles. I resort to using them in high winds and when it gets dark for much of the day in winter.
I do like to use spin bikes for tough interval work, though. Stuff that might be dangerous to do out on the roads.
Edited: 07/08/2012 at 08:50