If I do it by the serving, either nuking or putting the vacuum sealed bags in boiling water. If I know I'm going to be reheating a whole butt or brisket, though, I like to put it in foil whole, then reheat in a 200 degree oven over a couple of hours, until it's to serving temp. I think leaving the meat whole keeps it more moist. This has worked great for meals for the next Friday night, or if I'm taking it into the office (I'll use a crockpot then).
CBJ, some comps, a few awards, Certified Artisan Steak Taster.
XL Big Green Egg, Bubba Keg Convection Grill, Weber Kettle, Charbroil Infrared and mad livefire cooking skillz! :)