very old thread, but figured i'd respond.
I did HST exclusively and as meticulously as possible from around '04 all the way to mid '09 and saw some good mass and strength gains. I also was very anal about my diet and kept track of everything (i'm an accountant

), tinkering with different variables each cycle, etc. I have taken no prolonged time off from training since 2001 outside of the scheduled SD periods (9-14 days) in the HST program.
In '09 someone gave me p90x and i gave it a try. It provided by far the best results I've ever gotten. I, a trained individual, not only dropped huge amounts of fat (over 20 lbs -way more than I even thought I had on my body!) but also put on around 10-15 pounds of muscle
at the same time over only a 2 month period (again, I keep records of my weight, bf%, and measurements - so its not a guess). Totally changed my body. HST is great and I still use it when trying to pack on a few pounds of muscle, but if you haven't done p90x, even if you are highly active and trained, give it a try (with the diet!). I don't know why it worked so much better than anything else, but it does!
Can't recommend it highly enough.
If anyone else has tried the program in the 3 years since this thread started, please respond with your experience.