rb - i know that some people foil their pork shoulders at 160, 165 or whatever, then poke holes in the foil to prevent exactly what happened to yours. this allows the fat run out, but still protects the shoulder from getting any darker and also allows it to braise.
one suggestion: whether you foil the butts or not, or even if you decide to try the foil-with-poked-holes thing, devise a way to save the juices. most people simply use a foil pan underneath the meat. once those juices are de-fatted (put it in the freezer and allow fat to rise to top and harden, then remove the hardened fat), those juices can be added back into the meat for some really good, down-home porky flavor.