I'm personally a big fan of heavy to light sets, but I don't burn out with an increadiably light weight. Studies show that if you go too low (less than 40% of your one rep max) it actually does not release as much hgh (the desired effect of doing this), and it certainly isn't reqruiting the fibers you could be reqruiting. I like to do drop sets in the 5-5-5 rep range. Take a set to failure, reduce the weight to a weight you can only get 4 to 5 more reps with (with a 10 second or so break), then drop the weight slightly more to grind out 4 or 5 more. This is probably a better procol, since you are getting the benefit of doing higher reps, and the gycogen depeletion and hormone release associated, but you are working very close to your limits on each rep, thus creating enough tension to recruit alot of fibers. Just my 2 cc's worth...
On a side note, you can overtrain quite easily with these type of sets as well, so keep that in mind when outlining a program that incoroporates them.