Paladin tanking appears idiot proof, but don't be deceived. It just takes a different set of idiots to gimp you.
I find the worst sins are, in order:
1. People who CC. Frankly, before Kara, you will never need any CC, and it just risks causing a wipe by having the mob come out of CC at a low cycle in your mana where you can't get it back before it 1-shots the healer. I'd say half of the wipes I've had leveling are from CC. Once you hit the 10-mans, I don't know - I'll let others speak for that. But I've never seen the value before it when on a tankadin, and that INCLUDES MrT (when I first got to MrT we kept wiping over and over on the first few pulls until we stopped CC, and 15 minutes and no wipes later we were at the end boss - after that, we could always reliably speed run to the end by AoE tanking). What makes these guys the worst is that they are operating with good intentions and often are great players. Good CC is VITAL to working with a warrior or druid tank, and they know it. But... they lack experience working with a paladin tank, which takes a very different play style from the DPS. And they tend to refuse to see that.
2. Pull stealers. This one will gimp any tank... people with no armor who insist on doing the pull. When told not to, they ignore you and do it anyway, repeatedly. Invariably they stack a lot of threat, and then start running around in maddening circles kiting mobs away from you, and more importantly, away from any consecrates you drop. At best, you can taunt the mobs off of them, but the paladin taunt has very little threat to it, so you only get 3 seconds to stack as much threat as you can before the mob decides whether or not to break loose. Depending on how much running around they did, you may or may not be able to overtake them in that time. Quite often what happens is that in doing this they split the melee and caster mobs up, you taunt and get some of them, but they keep stacking DPS and running around and the ones that you don't get well enough 1-shot the healer 3 seconds later.
3. LoS pull breakers. This is kind of the same thing as the above. You set up an LoS pull to force all the casters and melee into melee range of you, and as the mob is running to you and through a consecrate you left while running to your LoS spot, they AoE blast them out there beyond your spot and it overtakes your initial threat before you have a chance to stack on anymore, leaving the ranged mobs out there and a few stragglers on you around that corner...
4. Huntards with growl. Yeah... while leveling you're going to face an endless horde of these. Some of them when called on it will say "ok, turned it off, only to have the pet growl in the next fight..." In my guild, I discovered to my horror midway through Kara one night that our raid hunter not only was using growl, but didn't even know it could be turned off... Well, it was actually 2 nights after the raid that I discovered it. The tankadin we used couldn't keep aggro worth a darn, and the group as a whole kept taking a lot of damage. She quit the guild. In chat I was talking with people about what I thought her gear had needed... We did a black morass run with my paladin and the same problem occurred... in discussing why, the conversation revealed that the hunter's pet had been using growl. The results of course, a pet taunting off kara mobs to a range outside of consecration, getting killed, and the mobs then going hog-wild. Or in Black Morass, doing that to those portal dragons and taking them so far from the portals that they reset... Myself on my own two paladin tanks, while leveling, faced this problem on roughly 3/4ths of all hunters that got invited to a PUG.
5. Non tank tanks. This one seems to happen most with shaman and warriors (warriors specc'd fury and arms that is) who think they can tank. They then enter the instance and do everything they can to prove they're a better tank than you. On occasion, I've had it happen with mages as well. Yeah, mages... As soon as some mages get their magic shield spells, they think they're AoE tanks... These people are the hardest to deal with (game wise that is, socially a quick fix is to boot them) because they use every trick their class provides to intentionally gimp you - kiting mobs, taunting, and even (at least 3 times for me), pulling half the instance down on you to show that you can't survive it (duh) - and therefore they should be the tank (nevermind that they couldn't survive it either).
6. Inattentive or Bubble healers. Yes, paladins often require more active healing than other tanks. Some people play healers because its the position you can play while being half AFK and having poor mana efficiency. Just let the warrior or druid have 1 health left at the end of the fight and all is ok. Others like to lesson the amount they have to do by putting a priest's bubble shield on the tank at the start of the pull, and then going AFK. But Paladins love a good active heal, even if its a small one - as it provides a steady stream of incoming mana. We're built to be able to go really low on health with Ardent Defender - but many healers go into panic mode when we're going down and rather than get active casting, they put a shield on us. Same overall mana cost from them, but no benefit to us... Honestly though... while healing for a tankadin is different, I at least, on my resto druid, find it -easier- even though it also requires more attention on my part. I'm not sure why... but I vastly prefer healing a paladin tank over any other tank, and find it easier to do so. In fact healing tankadins in heroics is why I first made my own tankadin.
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