Dungeon design (or, as Rowlf of Thrall calls it, "World of AOEcraft"):
One of the things that I noticed immediately about tanking 5-mans in Wrath is that it is typically much harder to LOS mob packs here than in BC. The nooks and crannies that you abused all the time to force mobs to move into a narrow area just don't seem to exist as frequently -- and where they do exist, they seem to be largely ineffective. Whether this is intended, I don't know, but it does make mob placement -- something that Druid tanks are very dependent on -- significantly more difficult, particularly in the following contexts:
1. Heroic Azjol-Nerub: The three mob packs before the first boss are very hard, bordering on impossible, to position correctly. The caster just never wants to move, and there's no truly effective means of LOSing him.
2. Heroic Oculus: I remember zoning into Oculus for the first time with the hall of dragons directly ahead of me and being utterly bewildered as to where the hell I was supposed to LOS a pull full of casters. Pro tip: you can't. You might as well let the mage tank, because he's going to be doing it anyway.
3. Heroic Utgarde Pinnacle: The gauntlet event for Skadi the Ruthless. This one takes winner, place, and show in exemplifying Swipe's problems as a means of holding AoE aggro. The moving trash spawns are not always, or even usually, within Swipe range of each other, which means that at least one or two of them will be well on their way to the healer by the time Swipe comes off the GCD. The usual means of dealing with this is to turn around and Feral Charge whatever got past you if it's more than one mob, or Growl if it's just one, exposing yourself to additional damage in the process and more likely than not losing aggro to DPS on the ones Swipe did manage to pick up.
Doing UP on heroic was actually the first truly disquieting moment I had in Wrath tanking. We had wiped on the event three times due to my inability to hold aggro to DPS while chasing mobs that Swipe had missed, and our healer was getting exasperated: "Guys, you can't DPS just because she's hit something. She's not a Paladin, she's a Druid."
I squirmed. Ouch, baby. Very ouch.
4. Heroic Gun'drak: Slad'ran (the snake boss) -- If game mechanics allowed for it, Gun'drak would have been burned to the ground two weeks after launch, and from a distance you would have seen a bear dancing on the rubble. Swipe and Demoralizing Roar seem completely ineffective at gluing any of the moving adds to you on their way to the healer, no matter how you position the boss.
5. Heroic Halls of Stone: The Brann Bronzebeard event is very unpopular with Druid tanks and for good reason. It combines all of the problems of the Skadi event (moving mob packs) with the very unwelcome element of two spawn points. The proverbial cherry on top is the achievement for doing this event without allowing Brann to take any damage, and most of the responsibility for this lies with the tank.
6. Sartharion (10-man or 25-man): If you're main-tanking Sartharion, no problems. If your guild is trying the event with drakes up and you're the drake tank, no problems. If you're the "portal tank" picking up a phased add with a drake up, no problems. If you're the unfortunate bugger who has to be the elemental tank, may God or possibly Ghostcrawler have mercy on your furry little soul.
7. Heroic Violet Hold: A lot of people have cited the annoyance of the Shadowstep mobs here. I haven't personally had too many issues with them -- although they are, don't get me wrong, incredibly irritating -- but they do require you to reposition all over again to avoid the additional damage from a mob you can't dodge.
8. Heroic Caverns of Time: Culling of Stratholme: If your group wants the Reins of the Bronze Drake off the Infinite Corruptor, AoEing down mob packs to save time is usually the way to go. Is this doable with a Druid tank? Yes. Fun? Not really.
As far as I see it, Swipe getting a 50% threat buff is going to be a big help on mob packs that can be positioned correctly -- and I would argue that a plurality of Wrath mob pulls do fall into this category -- and it'll give us time to get Infected Wounds applied to mobs in order to reduce incoming damage.
So, at least for me personally, the challenge is learning whether the uglier and more obstinate mob pulls can be affected by some trick of geography in the dungeons that I'm not aware of, or if the problem ultimately lies elsewhere. Swipe does seem to have a fairly dismal record with respect to moving mobs in gauntlet-style events or spawned adds. Further dungeon experience may render this a moot point, but for the moment, I'm not really all that eager to tank Halls of Stone again.