One of the interesting things about tanking is how the rest of the group automatically defers to you.
I've ran Gnomeregan a fair bit, and now know the easiest way to get to the boss with a minimum of fuss.1 When I'm on my tank, the group falls in behind me and we move through the instance smoothly.
On the other hand, when I'm on my rogue, generally people don't know which way to go, and the group stops for discussion. I can tell them the way to go, but they never seem to listen to me. Half the time we go in a crazy direction, and the group never makes it to the end boss. This happens even I am the nominal Party Leader.
Generally, my tank is perceived to have much more authority than my rogue, even though there's not a lot of difference between the two characters. It's like WoW players are trained to defer to the tanks.
Maybe it's just that the tank goes in first. Maybe being the first person in the battle confers an aura of leadership, in the style of ancient generals and kings.
I find the automatic mantle of authority to be a very interesting part of tanking, even if I'm not completely sure why the tank is assumed to be in charge.
1. Generally, always go left, and don't jump down. Jumping down with an inexperienced group inevitably causes more problems than it's worth.