im sensing a shrug lover here, am i right?
If you really want to beef up the upper traps, i wouldnt just do shrugs, im not trying to say its a bad exercise, but do heavy deadlifts, stuff like that aswell! Also, people who love shrugs, and cant contain their love for shrugs, often end up with bad posture, as regular shrugs (holding the weight in your hands) also fires the rhombes, which is a muscle that rotates the scapulae downwards (bad posture) and the traps, evne though they do counter the downward rotation by upward rotation, they are also scapulae elevators.
for more info: read this: Testosterone Nation - Push-Ups, Face Pulls, and Shrugs
just saying be careful mate and remember to balance the movements.
And if you really want big traps, get someone to teach you the olympic lifts, they do wonders for them!