What is interval training all about?

Interval training is all the rage at the moment, everyone wants to do it or if they are in the fitness industry then they want to get you doing it. The idea is that you alternate intense and easy bouts of exercise so you push your body hard but it gets to rest in between the hard parts. So you might do 5 minutes warm up then 1 minute of walking followed by 1 minute of running, then back to walking and so on. In this Fat Burning Furnace guide then it talks all about interval training as apparently it raises your metabolism for up to 36 hours after you finish exercising.