I've basically been doing HIT cardio for the past 3 months. Twice a week doing sprints, i.e. 5 minute warm-up, then 30 second sprint with a minute of moderate pace jog/walk, repeated 8 times and then a 5 minute cool-down. One day a week has been traditional moderate cardio.
I've also been fairly strict on the diet and consistent on the lifting. I've lost 30 pounds, so I'd say I'm a fan of it. (Yeah, I was a fatty - but now I'm NATTY. HA!!!)
Good description of it here:
Implementing A HIT Workout
There are many ways to implement a HIT workout. For instance, I like to sit on the recumbent bike and warm up for 5-minutes. After my warm up I then execute a hard minute sprint and then rest for 2-minutes going at a slower but challenging pace.
I perform 5 sets of the 1-minute/2-minute combo (total of 15 minutes) and then I'm done. However, there are many other ways you can play around.
For instance, you can do 10 sets of 20 seconds hard and 40 seconds slow. If you notice, I like to perform the active rest for twice the amount of time it takes to perform the sprint part.
If on a treadmill you can run, and then walk, or alternatively you can play with the elevation as well. Use your imagination and have fun.