I tried multiplayer, but the problem seems to be that some other people are just jerks and enjoy killing and destruction which are totally counter to my goals. I played for a couple of hours to build and mine, only to come back the next day to find my house destroyed and my shit gone. meh. I know one of the upcoming updates has lockable chests so at least people won't be tempted to steal my gear. Maybe I'll give it another shot then.
While I was there though, I saw a lot of TNT being used. I've never even made TNT before so I was a little curious. I've seen it create some pretty impressive explosions so I figured I'd see how much gunpowder I had from creepers to make explosives. Turns out I could make about 10 blocks.
I picked a spot near the bottom of my sub oceanic mine that I felt had been pretty much exhausted. and loaded all the TNT into a little space and set them on fire. Good times ensued! But nothing very exciting. The hole it created wasn't that impressive.
So no matter what I do next, I'll probably also be building a monster trap to aid in the collection of much much more gunpowder from dead creepers.
http://www.youtube.com/watch?v=AzAofFVTTGQ