Just look at this... It's Marathon World Record holder Haile Gebrselassie "jogging" on a treadmill. When you see him running in the street, it's hard to get much of an idea of how fast he is running, he makes it look so easy. If you had never run on a treadmill before, you could be forgiven for thinking that there was nothing to it after seeing a video like this.
By the way, in case you are wondering, he is running at 4 minutes per mile (no, not per kilometer). What impresses me the most is that his stride is so long, he almost runs out of treadmill.