Check out this article by Steve Magness, Cross country coach at the University of Houston, former Assistant Coach for the Nike Oregon project, Masters of Exercise Science.
This has been a bit of a UK fad since the program aired here last year, TV journalist Andrew Marr suffered a stroke while doing HIT on a rowing machine.
I read a newspaper article, supposedly promoting HIT, where the, previously untrained, journalist was tested, did 6 wks of HIT, was retested, had 8 wks with no training, then did 6 wks of steady state aerobic training and was retested. He improved after the HIT, but he improved 25% more after the steady state training!
People used to train this way in the 1940s, we've learnt a bit since then, and guess what, things just aren't that simple.
HIT may improve your VO2max, but there would be little improvement in low end endurance performance ie. backpacking.