Bill,
As usual, Ming Thein makes many good points, and the equivalencies he sites betwee Micro 4/3, Full Frame and Medium Format digital under real world, hand held conditions are enlightening. His advice that bigger is better, if you are willing to lug an appropriately sized tripod or lighting equipment is also sound.
He excluded cost from his analysis and stated that he was doing so. But cost is highly relevant to most of us who are not professionals with a chance of recouping the cost relatively quickly, if we have run the numbers correctly and have made reasonable assumptions. Even if money were no object, realizing the full potential of 36+ MP sensors, be they full frame or MF, is likely quite difficult. There is also the practical consideration that many of us don't print as much as in the old days and don't print as large, so the full capability of the high megapixel sensor may rarely or never be used in the display of one's work.
One point that Ming Thein made is that "big and cheap" these days means medium or large format film (i.e., cheap relative to MF digital). Many of us here are still film people or mostly film people, so this point is salient for us. Personally, for the kind of photography I do, which is landscape or urban landscape or slow moving animate things and mostly black and white, medium format film seems to hit the sweet spot as far as image quality, "look" (due to the lenses), portability and, in this post-film market, cost. Large format was just too much to carry. 35mm is still great for many applications too, but lacks the distinctive look of medium format for the kind of photography I do. Street shooters, sports shooters, etc will almost certainly have other ideas that suit them better.
