Funny this comes up today, a few hours ago I reached the point in Terraria where you have to go kill the Wall of Flesh to advance, and although I knew he was death, I did not know to what extent.
My first attempt ended with me taking out about...4% of his health before plummetting into a pit of lava and proceeding to drown/burn.
I anticipate trying times ahead -.-..go figure all the awesome stuff is only available after he's dead. If nothing else, its a cool and creative fight.
Your actually supposed to create a bridge/arena to fight him in beforehand like most of the games bosses, but to a much greater extent, which simplifies the fight greatly, this process takes atleast a solid hour, but trying to just wing it is a serious pain with the gear your supposed to have at that point unless you utilize a very specific strategy.
http://www.youtube.com/watch?v=f0LWWyg4bzM&feature=related
This guy. You can use assorted flight items/potions to evade him too, or just really jumpy/travel related equipment, regardless you just have to be able to stay on the move, above lava, and not crash into walls xD.