Hmmm, my wife just finished another room today with polyurethane. It looks awesome and the timbers are glass smooth. I measured the 10x10 posts and they are consistently 9.75 x 9.75. The 3x8 braces measure 7.5" in the 8" dimension... if that gives you some idea of the moisture content. The checks in the timbers are deep and wide and probably have almost as much surface area for moisture to escape as did the unfinished timbers before they checked. We're wagering our house that the timbers won't rot from the inside.
FWIW, I think unfinished timbers and oiled timbers look great too... I love the unfinished timbers in my barns. Especially the ones where the cattle rub them smooth. I just can not, for the life of me, figure out how to keep them clean in my house (the unfinished timbers - not the cattle!).
-Thomas
