Well I found out the destructive power of approx 300 TnT. Half tempted on filling the crater I made with about 10x that and seeing the results. Although I will need to figure out a safe structure I can hide in because last time I hid behind a stone wall only to see some of the tnt blocks hover over my head before exploding.
Oh and to give some reference to how big the explosion was there are some sand blocks to the southwest of the explosion that seem to have traveled 3x the distance you can shoot an arrow.
Edit: Well there was a cave at the bottom of that crater filled with more creepers than you can shake a stick at. I got bored and filled the bottom cavity with 1200 TnT. Now there is a massive underground cave. :P Might go exploring after a while but not looking forward to clearing out the mobs that filled the hole. Going to probably keep it like it is for at least a week, in case someone wants to go take a peak. :P
Edited, Jul 6th 2011 2:47pm by Criminy
It's best to play around with TNT on a single player game, that way when you blow a up huge part of the world you don't leave a massive deathpit for anyone to wonder in to. Also, the only real protection from TNT is to either create a fuse of sorts by laying down a long string of it so you're far enough away not to get blasted, or lock yourself up inside a small room made of obsidian. I messed around with it for a bit myself. I would dig straight down to bedrock, fill up the shaft along with caves I found on the way down, move six or seven blocks over and do it again. Once I had twenty or so shafts I'd set it off and blow up an area too large to see the other end, straight down to the bottom of the world. It's amusing enough, but gets old after awhile.