Zorbs already mentioned this, but I feel like it bears repeating.
Hands off the rail, my friend.
Holding on to the rails compromises your form and your calorie burn, and makes the whole workout less adequate. You get a better, more effective workout in less time if you keep your hands off the bars and move your arms while you walk. My trainer once told me (and I don't know how true this is, but it makes sense to me) that you can cut your calorie burn in HALF by putting too much weight on those bars! Think about it. Go grab your scale at home. Put it next to a counter. Stand on it. Got your weight? Good! Now, get off, get back on, but this time... lean on the counter.
How much weight did you "lose"?
By leaning, you're cutting your weight, and the effort you're putting into it, by carrying your weight in your arms. Don't cheat yourself!
Here's a great article here at Sparkpeople that will help you get the most out of your treadmill workout: www.sparkpeople.com/resource/fitness_artic
And here's one that will help you keep your treadmill workout from getting stale: www.sparkpeople.com/resource/fitness_artic