Potatos taking over? I guess I've never seen that, at least when compared to various squashes, melons and cuccumbers (sp...).
Potatos are notorious for coming to the surface and getting sunburned, so oftentimes it doesn't matter how deep you plant them as the new potatos will develop where they want. 6" sounds pretty good, though. I actually prefer to plant shallower and slowly mound dirt as the potatos start to show on the surface. This makes for easier digging when you are ready. I also plant them closer together than most growers as this provides some shielding from the sun (perhaps 12 inches apart). Yield takes a minimal hit.
As far as growing, they have to be one of the easiest things to grow. Since they reside underground, they can tap into the moist soil down 6-8 inches throughout the summer months. Water them 3 times a week during drought season and you'll be set. Just as with grass, overwatering will promote shallow root growth, and in this case, more potatos deciding out of the dirt is better than in...
Other than that, don't plant potatos from a standard grocery store. Organic is typically ok, but bulk taters are normally sprayed to slow sprouting. They will still grow but yield is low. If you cut the potatos into multiple pieces (good if large), make sure each piece is 8 cubic inches (2x2x2). This seems to be the sweet spot between enough feeding mass and digging up a partially rotten mass along with your new taters.
The last thing I'll say is grow potatos you find a treat. For me, I grow red varieties as I love baby reds. Just like sweet corn, you can't beat picking it an hour before dinner. As for baking potatos or other large varieties, the reward just isn't there. The fresh ones from the store or farmers market taste the same to me.
Sorry for the rambling.
