I love to tank. I really do. The thing is, that I see the 5 man group in an instance as a team in which everyone plays their own position. Like in an ice-hockey team.
For me the tank is the goal keeper. He's the one who states that the 'Buck Stops Here', taking care of the rest of the team and securing that they can do their job properly and as easily as possible. Tanking is simple and easy in principle, requiring only some sense of spatial awareness on top of good sense on the skills in her/his disposal. The gear is a nice addition and brings more survivability to the mix, but it's not the thing that makes a tank, really. It just makes the job easier by far.
The part of the DPS is actually the hardest, when you think of it. The DPS are the rest of the field players, the front line assault team creating the damage to down the mob or boss. What makes the job of the DPS hard is the fact that the threat the tank is generating has a limit, while the limit of the damage DPS is generating is much higher. The most of the problems in tank losing aggro isn't from her/him being a slacker, but the DPS being too eager to shine in the damage meters. The thin line between 90% aggro and aggro break should be the DPS's concern, not necessarily the tanks, because the tank can do only so much to remedy that. Instead of staring at the damage meter, the DPS should stare their threat meter. And keep themselves out of trouble by not stealing the aggro from the tank. In a good ice-hockey game the players make sure that the goalie has as little to do as possible: the same should apply to the tanking and dps. The DPS should take care that the Tank has as little extra to do as possible to ensure smooth run.
Actually, the healer is not playing in the hockey field at all, but is at the back, handing out the drinks and keeping the tank up and the DPS doing their part. The gentle rub from the healer to the dps should be enough to keep the game rolling, not the stitching or rubbing the sores of the over aggressive player. Healer is the most important piece of the puzzle, even though her/his contribution is the least easy to measure.
So why do I love tanking?
It's staying on top of the game, doing your best to keep the encounters rolling smoothly and doing your best without a measurable meter to track you down. DPS is fun and furious competition in reaching as high as possible in the damage meter: the competition and measurable success makes it so much fun in it's own right. When the DPS takes their aggro generation seriously, even a less well geared tank can do their work in a heated situation. As long as the aggro doesn't go wild and the tank can concentrate on keeping the mob/boss on her/himself, the game flows smoothly.
As a tank you are your own critic, you are the only one who can really tell how to improve and how to do the thing you do so well even better the next time. It's not about perfecting the rotation, or about perfecting the button sequence. I love the fact that I can analyse my performance on my own, find my own lacking skills and find remedies for them.
The worst part in the current speed running of the heroics (when you have gotten that far in the game) is the fact that you really cannot learn anything from the runs. The DPS is acting like a ice-hockey team's primadonna, doing everything on their own, without worrying about the rest of the team and complaining about the performance of the rest of the team when they encounter problems. The healers are yawning through the instances until the fore mentioned primadonna strikes an odd chord and gets almost killed. And there are only so many 5 man instance bosses who can cause problems to a decent geared tank anymore, as long as the healer can take it without falling asleep.
I believe the instances would run even smoother and provide more fun, if people would just remember their spot and follow the cue of the tank. It really doesn't hurt to be polite and play as good as you can in any group you may encounter.
It really pays later on. One way or another.