Shrugs are a great way to work your upper traps. Be careful, though, because they're easy to do incorrectly. I see a lot of guys rolling their shoulders backward as they shrug the dumbbells up. Don't do this! Pull the weight straight up, then move it straight back down.
It's also important that you're using your traps—and only your traps—to do the work. Try to keep your elbows as straight as you can. If you feel yourself swinging or using your lower arms to help you lift, then you need to drop the weight.