travco - .30/06 would be my choice too, if i had to choose between the two ~ ;)
fencesitter, thanks for bringing the discussion back on track. i'll offer my opinion and thoughts on the matter, then i am sure others will follow:
regardless of WHEN you place the probe, the WHERE is easy: you place it in the middle of the meat where there is no fat and no bone nearby to give you a false reading. the reason for this is found in the basic fundamental of barbecue:
there is cooking meat until it is done, and cooking meat until it is barbecue. technically, at 160, the meat is done (and all the little cooties are dead); but the fact remains that there is a lot of connective tissue, fat and collagen left in the meat. this is the stuff that makes pork shoulder, brisket, ribs etc the nasty, cheap cuts of meat that they are - they are hard to cook normally because of all of this stuff. if you were to set them in the oven at normal roasting temperatures, or fry them in a pan at pan-frying temperatures, they will be done long before this "stuff" breaks down, melts or whatever you want to call it - in fact,they would be burned AND dry as a bone, not to mention tough as an old boot.
by cooking large masses of meat at lower temperatures, you are giving the meat time to break down all the stuff while still remaining moist and not getting too hot too fast; in fact, the melting of the collagen and fat actually contributes to a moist, tender finished product that is now barbecue. this is why traditional barbecue meats are the large, fatty gristly things such as pork shoulder, brisket etc. ribs also fit into this category due to their make-up.
with brisket and pork shoulder, you are going up around 185 and in the case of pulled pork, up around 200 degrees. this is far past "technical" done but right into "barbecue" zone where all of your connective tissue/collagen and most of your fat has rendered out. this is the difference between "barbecue" and grilling, which is done hot and fast for tender cuts of meat such as steas, etc.
now, back to the probe. you want to place the probe in the thickest aprt of the center as mentioned above because this is the last point in the meat that will be done with its cooking, melting, and general transformation from meat to barbecue.
hope that answers your question. there is a whole lot of science involved but as i said before, we're cooking meat here, not building a space shuttle. my best advice is to put your engineering books away, start a fire and slap some rub on something. a whole lot more will be learned by doing it rather than reading about it.