I've injected my last few Butts and Briskets and I really like the results. It took my barbecue from passable but a little dry to stupidly tender and moist. I live in the desert though, so any aditional humidity really helps keep things from drying out. Lots of people are obsessed with dry heat but I suspect they're from humid places, cause I have the opposite problem.
I really like to inject my butts with Worcestershire, apple cider and sometimes vinegar. The only other way I've gotten that flavor was by soaking a butt in a large amount of cider vinegar and Worcestershire overnight (from a recipe in Smoke in the Mountains), which was expensive, wasteful and messy.