I made a testrun with a program that gives the ability to modify your inventory, giving me max tnt and all the other stuff to try out ( just go to the minecraft forums, it's callen MineEdit ), and I found out that TNT is only really good to mine sand imo, as it has a bad habit of destroying part of the ores you want to have. Like if you use it on coal, you'll get maybe 3 pieces instead of the 6 you'd get digging by hand.
I also don't like lava furnaces so much, as the fact that you lose the bucket, kinda makes them really expensive.
The green blobs are slimes, and the orbs they drop have no use.
Also, if you would like some slightly better graphics, over at the minecraft forums they have tons of HD graphic packs.
Here is the one I use, called mixcraft