I've had my Champions in for about 100,000 KM (60,000 miles). Not a single misfire. I'd say they are great when you get a good batch of them. I know a lot of people have had bad batches though...
I am getting ready to swap my plugs again. It's nice to know the Champions won't snap off, but I am going back to motorcrafts just to see if there is any difference in the butt dyno. Likely not, but maybe I might notice some MPG or something.