well.. I can talk behalf jnn about this subject atleast, and HIT works... it just does.
Killing your self with lets say 7 150m sprints after jogging 5 miles gives you a crispy looking abs. Jogging before sprinting to get you warmed up, it's pain in the ass to sprint out of cold.
I haven't done cardio in ages once again because the whole "cardio" thing is boring in my oppinion, but it works.