Brian is right. You definitely don't want to be in the frame when that critical piece or joint lets go. We always use come-a-longs to pull and rack frames before driving or drilling out pegs. It helps "unload" the joint the peg is in. We also always nail diagonal bracing to the bents and walls as we go to help keep things where they are as the pegs come out.

I'm not a big fan of peg drilling. The damage done to the joints is less problematic if your just demolishing a frame, but you still run the risk of leaving pieces of the peg in the joint. It's pretty astounding how strong a 1/4" sliver of peg is! A hollow pointed peg driver and a good 3 pound sledge gets the job done. Where there's a problem, like blind pegs, a drill may be the only answer. If the peg hole doesn't seem to go all the way through, look for a little hole left behind by the screw tip auger. Very often there's only a 1/8" piece of wood in the way which pops right out when you hit it with the peg driver.

Probably the most overlooked part of tearing down a frame (other than calling someone who does it for a living) is figuring out the way it was raised up. If you can determine the order in which is was assembled, you can reverse the process and save a lot of hard work. It also means a lot of the pegs can be left in until the bents are lying on the ground.

Good luck, and wear a hard hat!