Just finished my first "True" deep mine run, and was the rewards were great. At one point, I completely abused the 1st rule of minecraft and ended up in redstone heaven, and was promptly in cave spider hell. After that, I came across a skeleton spawn room with a couple of chests that had eight diamonds in total. After it was cleaned out, it was sealed and marked. After a while of exploring, marking, path laying (left a strip of dirt in the left side of the passages) and squeeing in glee at the amount of ore that mine has in it, I went back to my forward outpost and dug straight up, knowing I'd hit the swamp somewhere near my fort.
Imagine my surprise that after three hours, countless tunnels and kilometers walked and a proverbial fraktonne of mobs slain, I end up not 40 feet from my perimeter wall and main door....but under the surrounding swamp. A quick dirt square and a bucket o' lava soon solved that.
Next step to be taken tomorrow?
*Secure the mine access properly and make it easier to get to (probably by expanding the wall).
*Set up a powered rail system so that I can get to the abandoned mine.
*Kill stuff
*?????
*PROFIT!!
Nothing compared to the stuff that you guys have done, but considering that after my first attempt left me with a VERY rational fear of Endermen and the deeper levels, I am bloody proud of myself for not dying while wearing only iron body armour and leather trousers.