Might not seem too exciting, but one advantage I found is this... Even if you're getting tired, you can't slow down on the treadmill. It is kind of like having your own personal coach - forcing you to continue to the end of the interval. Also, you know your pace is consistent! It really was a great workout. Here's what I did:
Six Half Mile Repeats with Quarter Mile Recoveries - Each half mile was 3:24. I did my recoveries in 2:12.
It was nice to get a feel for the pace though I now know that treadmill pace feels much different than outside pace. I was very happy with how I did today. My total distance was 6.75 miles.