It's hard to do sometimes, but you gotta leave 'em in till they're done. The temps give you a pretty good idea, but there's a lot of room for variation. Checking with the probe just for ease of entry is the best thing you can do, IMO. I always cook butts and briskets at 250 plus or minus 15 degrees, but I also mop like hell after the first five hours or so. Everytime I do anything to the cooker (add fuel, check temps, fill water pan) I figure I might as well mop. It's served me well so far. I d cut back a little bit toward the end so the bark crisps up a little.
Weber Smokey Joe
18" Weber Kettle
22" Weber clone kettle
Curb-foundling char-broil gasser
WSM: Assembled! First cook: 8/25/06
Fanatical devotion to the Q