Mined a 10x10 pit from 70 to 5.
Results:
Max mined blocks: 65x100 = 6500
Stone: 5032/6500
Dirt: 752/6500
Iron: 103/6500
Coal: 340/6500
Lapiz: 3/6500 - WTF
Diamond: 41/6500 - Found at layers 15-13, 11-10, 8-5
The other 229 blocks were a cavern. One cavern in that square =P
Either way, it's a lesson to us all. Don't mine straight down for 4 hours with stone tools. It's not worth it.
However, I do have a seemly endless supply of stone, iron and diamond tools now =).
(+ 3 blue wool

)
EDIT: I'm surprised @ No redstone