Okay, I was tanking the adds on the 10man heroic Anub fight last night, and I had aggro issues for about the first time I can remember.
The problem wasn't keeping them on me once they got in range - as a paladin I have excellent threat, especially against undead. The problem was getting them to come to me.
If they both spawned near eachother, nothing was wrong. I could shield one, and melee the other, then move them together, and get them on the ice before they burrowed.
The problem occured when they spawned apart from eachother. I used to shield one, then run to the other to pick him up. The problem is that I didn't have time to get them both together before moving onto the ice or they'd burrowed, and once I was on the ice, if a mob was more then a few seconds moving away from me, I'd lose aggro to the healers, and taunt didn't last long enough for me to get them into a position where I could melee them.
Since I was on the ice, and the mobs eat through healers pretty quickly, I only have time to use one global cooldown, and moving to the add just wasn't quick enough due to that and the fact that the other add could burrow.
I asked the tank to try and tank Anub near his initial position, but since we needed the incidental AoE the raid provided to be able to get the adds down quickly enough, that wasn't always an option, and I got into a position where adds spawned on opposite sides of the raid, where I HAD to pick up the one moving to the tank and picking him up good, or the debuffs would endanger the tank.