Burn More Calories With Interval Training
Interval training not only increases your metabolic rate during a workout but also keeps it elevated for hours afterward, burning more calories even while you're sitting on the couch. A study published in Medicine & Science in Sports & Exercise found that subjects not only burn more calories during interval cycling than continuous cycling but also burn more calories in the following 24 hours. Other studies, in which subjects ran instead of cycled, also found higher post-workout metabolic rates after interval workouts than after continuous workouts.
Jason R. Karp MS

Yup, read about this last
Yup, read about this last fall. Started to implement it as my running routine. I used a training technique called, 'fartlek.' Sounds pretty funny. It's actually Swedish for 'speed play.' You just let your body decide how quick to run based on how you feel, followed by a rest period using the same philosophy. It just requires that you be honest with yourself about what your limitations are. It's not quite as rigid as Interval Training, but both have their benefits. In fact, I'm using it tonight! Can't wait till the weather gets better.
Works for me
I've been doing it for about a week now (twice a week in the gym) and the only issue I've found so far is the difficulty in programming the treadmill! Apart from that I've found I can go for longer and don't over-heat (poor air conditioning in my gym) anywhere near as much.
One thing that I would ask, however, is what's the best intervals to use. I've tried 1 minute on 1 minute off going from 13.5 down to 5 on the speed setting as well as 2 minutes on and 2 minutes off. So far the 2 minute version appears to be expending more calories.
With Fartlek, the intervals
With Fartlek, the intervals are all based on your honest view of what you're capable of. Just don't sell yourself short and stop an interval cause you feel like stopping, push yourself a bit. With HIIT, High Intensity Interval Training, it's strict. You must adhere to a regime with basically strict timing. Sounds like you may have found your niche though. Just keep working on your overall time/speed. Good luck.