If we choose Challenge mode before getting into an instance, we’ll have a timer appearing as soon as we enter the instance. Depending on our speed, we get medals at the end, along with pets, achies, items for transmogrification, and most importantly, we get a high score, so we can see who is the 1337est on the server. Gear will be normalized, so there will be no unfair advantages against others.
It would be great if the same system would apply to raids as well. We can hope for that, since the devs thought about this too. “Who can plow through Firelands in the shortest time? Game on!” ^^