Pork butts are forgiving, but briskets are ornery. Shoot for 1.5 hours per pound at 220F, with an internal temp of 185-190F. You want a slight tug on each slice to pull it apart (think perfect pot roast), and not mushy fibers. Wrap and rest in a warm cooler for one to two hours. The WSM forum has a good tutorial on trimming. Don't forget to "mark" the grain with a notched cut before cooking, so you have a guide for slicing your blackened beast.
The fat content and the toughness of the meat varies greatly from animal to animal, even within USDAÂ grades.
I don't inject butt or poultry, but I find brisket profits from injecting a high quality beef stock with a touch of worcestershire.