All, I shoudl have mentioned that I tried brining a whole butt a couple years back. I brined it for 48 hours an d found it only penetrated about 1.5 inches into the meat. The only reason I think it worked this time was becuase I had quartered the butts, and there were no pieces over 3 inches thick. So the strong brine I made was able to penetrate thoroughly. The brine water when I drained it was a lovely pink color, and the meat tasted a little hammy and the flavor was ehanced from the salt. It was good. However, trying to brine a whole butt will probably just disappoint you.
These pieces were too small to deal with injecting in my opinion and is why I brined them instead. I think injecting a butt is a way to "brine" quickly. It gets a salty-solution with optional flavors added down into the meat quickly making it more moist in the end. I'm of the opinion that injecting a solution with salt into the meat gives you the benefit of brining by making the proteins wrap around the water molecules in the inject solution and trapping them in the meat while it cooks, the same as brining, except you are increasing the initial surface are the solution is exposed to by putting it inside the meat as opposed to waiting for it to fully absorb.
My brining in this experiment was basically similar to an inject in my opinion, but without any sweet or flavorings added. You can add those to brines as easily as to an inject, and a lot of people do.