I am not a fan of doing beer can anything but I've smoked or smoked-roasted many a duck. For ones I raise I brine because they are lean but for store-bought I don't bother. I like duck breast medium-rare so I'll smoke a duck for a little while then pull, cut off the breast, return the rest of the duck to the smoker and crank the heat to finish (I like crisp skin). The breast I'll finish on the grill like Clay does.
Domestic duck from the store is quite fatty. Piercing the skin all over prior to smoking will allow the fat to drain during cooking. If I'm smoking the duck to use in something else I don't do this.