My Guardian is now level 42, and I've tanked all the flashpoints (except Colicoid War Games) up to this point, and the AoE taunt has to be one of my least used abilities. Because of its relatively long cooldown, I've used it as more of an "oh ****" button for quickly grabbing aggro from multiple mobs should I lose it.
Having tanked in other MMOs, at first I was desperately trying to use the same techniques, getting aggro on everything and holding it - if you're facing a large pack with a couple of elites, strongs and then some trash that's very difficult. The logical tactic is usually to kill off the weakest enemies first (unless their damage is so low it makes no difference keeping them alive), that means that its not really necessary for the tank to try to pick up those not-so-hard hitting normal (or even strong) mobs - they will be dead quickly enough anyway. That means you can focus on keeping the aggro on a smaller number of harder hitting enemies. I usually do that switching targets after every two sunders, but that can change depending on the situation of course, and using the single target and AoE taunts when needed, not on every CD.
I'm sure there are other ways to be an effective tank, but so far the only wipes I've experienced are from bosses where we didn't know that tactics and had to figure them out as we went, so I think this is pretty effective as long as the DPS are on board and know to kill off the weaker enemies quickly!