HIT is just one way to skin a cat. Personally i actually like being in the gym so would rather go more often than once every seven years.
I did a Mentzer program some years ago and i got better at using tempo, somewhat more muscular, and stronger (when on a HIT program). My explosive power for 1RM strength and the like took a huge fucking nose dive.
It was alright though, i quite liked the fact it was way different than other bodybuilding regimens. Even though Mike was insane and a cokehead i respect the guy for putting a middle finger up to Weider and doing his own stuff. At least he could back up his training philosophy with a little more than supplement and magazine sales. He certainly put more thought put into his methods than most 5-day-splitters.
Also, don't believe all that hardgainer crap. There is 100% no such thing. How the hell can you even measure your metabolism? So called hardgainers are generally just under-eaters or people who don't know what the hell they're doing in the gym.
Man i'm cranky thismorning.