Is no one going to state the obvious? More often than not, the dog gets basically a revenge kill after another player kills you. Nine times out of ten my dog does nothing other than growl if it senses an enemy and gets a kill after I'm dead. In regard to the "run-around-the-map-kill-everyone-no-gun skill" comment, the dog tries to find you after you spawn. It doesn't run wild around the map all the time, it'll always be nearby whoever calls it in.