Some of us are not fans of treadmills.
Check out her humorous post about a dislike for treadmills. However, treadmills are a great tool to use during bad weather and the winter months.
What I try to do is mix using the treadmill with running on the track of our fitness center. That offers a little more variety. Treadmills can also help push you if u are trying to build your speed.
You can also do programs that you might not otherwise do that challenge you.