I've never done it in a crockpot. Please post your results.

I've done many on my backyard smoker - an 8-10 lb Boston Butt takes about 10-14 hours (depends upon the ambient temperature) at 225 degrees to reach 185 internal degrees. That's fairly high for most meats - they would usually be dry, but the pork has plenty of fat to prevent that. If you approach that temperature slowly, all the connective tissue and fat will have dissolved into a nice juicyness without any discernable fat. We don't trim trim the fat cap, but put it on top so juices distrubute through the meat as it cooks. We also use a dry rub heavy with paprika, pepper, and brown sugar, and we first coat the meat with plain yellow mustard to hold the rub on. I add wood chips to keep it smoky for at least the first 6 hours. After that, not much more will enter the pork. Oh, and my smoker has a water pan to keep things moist.

It's important to get the Boston Butt, not the picnic. This is basicly the front shoulder of the pig. The picnic is lower down on the front leg (back leg becomes ham). The Boston Butt, also known as blade roast, has much better texture, absence of silverskin, and a single bone that literally falls out or pulls out with your fingers if the meat is cooked properly.

The main thing with Boston Butt is to get it to 185 or 190 degrees, but do it very slowly. All fat globs and connective tissue will turn into wonderfully moist and flavorful meat.