Have a look in my mine, the entrance is near the middle of my wall. The pattern I use in that is apparently the most efficient for covering a particular area, i.e. the minimum number of tunnels needed to uncover all potential mineral nodes, with the least amount of travel. I'll try to make a diagram of it, if it isn't clear from walking around inside it.
As for the grafting thing, it definitely affects what you try to build if you know you'd have to collect all the materials first. I wouldn't have been able to build a valley in the sea if I'd had to collect all the wool first.
(wool for putting in place of the water source blocks, of which every block of sea is one. Replace water, burn wool, voila, instant hole-in-the-sea)
EDITED: 31 Aug 2011 15:35 by CAER