i know this has been done on many blogs before, but i ate some of it this morning and it was worth getting up at 5:30 to bake and rest it before going to work. wanted to reiterate that it CAN be done, DELICIOUSLY, even if Jim Lahey does not really recommend it (or Bittman's 4/8 hour version).
i substitued 1/2 c. whole wheat and 1/2 c. rye for 1 c. of white flour, added a pinch more salt, and since i didn't have instant yeast, stirred scant 1/2 t. active dry into 100*F water and did the usual yeast thing.
it turned out with the characteristic crisp crust, large holes, and soft interior, though i think the crust was chewier than normal.
next time i want to add more whole wheat, but keep the rye. rye is good stuff.