I think if done properly there is nothing really unsafe about stacked frames, just that most we have seen were hillbilly hacked together POS's.........however I also see absolutely no benefit to running stacked frames.
If you have two frames sitting right on top of each other you get maybe 6"??? Not like it gives you 36" of lift or something...with my point being it's pretty easy to get the same amount of lift by "normal" means and I'm pretty sure it's a lot easier and quicker to bolt on a 4" suspension and 2" body lift and you probably won't even have to modify any component to do so.
For the comment from the guy saying his truck "rocks" in the mud...please explain how your stacked frames make it perform so much better. Is it the extra "strength", or maybe just the extra weight that makes it go better in the mud than everybody else

Or maybe because it rocks because you are comparing it to trucks on bald 31's?????