Lots of good advice/comments in this thread. If you want to finish your pork butt faster (with the probe as close to the center the grate as possible but still 1.5 or so away from the meat) you can run a little hotter (up to 275*) or as JWorden has suggested, you wrap that sucker up after it's 160F or so and the bark is set.
I always wrap, and always check the bark but scratching at it with a fingernail. If it's not set, a light scratching will remove part of the bark. If you scratch and the bark is firmly attached, then I double wrap in HD foil, and put a couple of tablespoons of beer or apple juice in there. With wrapping you should get through the stall in about half the time. I would usually plan for 10 to 12 hours actual cook time on an 8 lb butt (in favorable weather).
*You might need to foil your pan and run dry in order to run higher temperatures. Dry pan vs water in the pan is a somewhat controversial topic.... I normally run dry so I don't have the "wet clean up on aisle 5", and my butts normally turn out pretty darn good. Finally, running hotter is more difficult when the weather is against you, and your fighting wind, cold, or rain.