It seems like my colleagues have pretty well covered the bases.
Bill Kier is correct in that timber shrinks much less in the longitudinal direction. Another difference in timber frames vs log homes is that the window and door openings are not cut in the timberframe itself. The openings are in the (usually more stable) enclosure system such as stress skin panels. So whne the frame moves, it does not immediately and directly effect the openings as would happen in a log building.
Joel's point is well taken on the difficulty of both obtaining and working dry timbers. I have discussed the kiln dried oak with one timberframe shop that did a major project uaing that wood. There were numerous tales of burnt drill bits and rolled chisel edges. The same shop also does a lot of work in recycled timber. The cost is higher than green timber, and again, it is more difficult to work.
The trade off being that the end result is more stable, and, at least with recycled timber, more socially responsible.
Another good book on the movement of wood is Bruce Hoadley's "understanding Wood". Included in the text is a method for calculating the shrinkage of wood.