A lot of people seem to think that there is something wrong with warriors in WotLK, but in my experience the flaw often lies in the rest of the group or in the player. DPS lately have an unreasonable desire to go all out on targets without even allowing the tank to establish aggro, while blatantly ignoring any marked kill order. It is important to realize that this behavior will make it difficult for any tank. Of course on single target or boss pulls, any decent tank will find it easy to compensate, but on AE pulls involving elite trash, this can be a major issue. I've found that simply speaking with the DPS and using vigilance on the worst offender solves the problem around 80% of the time.
In spite of my above statements, warriors do need to realize that there are some positions best filled by other classes. We will never be able to hold aggro on large trash packs as easily as a Paladin can, nor should we be able to. In a raid environment, see to it that you have a Paladin as your OT for trash packs and AE fights.
Now there are of course some situations, such as heroics, where you will be the only tank. In these situations, you need to make the most of the AE tanking abilities that you do possess as a warrior. I'll give a few tips below:
1: If there really are too many mobs for you to tank, utilize some CC...it is there for a reason.
2: Spec down to deep wounds in the arms tree and glyph your cleave to hit and extra target. Be sure that you have improved TC. If you do not have these for trash/heroic tanking, you're doing it wrong. Is cleave a crutch as some people say? Yes. Does that make it bad if it allows you to succeed? No.
3: Charge casters and stack the melee mobs on top of them before your shockwave. Stacked mobs are far easier to tab through. Yes, you're a warrior. You DO have to tab through individual mobs. If you must ranged pull, use your heroic throw to silence the caster. Use bloodrage in place of charge in such situations.
4: Gear for what you are actually doing. If you are tanking trash/heroics/OTing, gear for more DPS stats/SBR/SBV/etc. You only gear strictly for avoidance/stam as the MT (you still need reasonable threat stats then as well). While it is possible to use a balanced set of gear, you should ideally have two separate ones in my opinion.
5: Finally, if you are truly fed up with warrior tanking, but you still want to tank, simply reroll. There is no reason to keep playing a class that doesn't work for you.
6: Ask rogues/hunters for help. MD and TotT make a world of difference on a large pull. Ask DPS paladins/dks not to drop consecrate/D&D if it is making it difficult to hold aggro off of them (They probably shouldn't have been using those abilities anyway).
7: Make sure that the DPS/healers all utilize threat meters and stay behind you if possible. Healers/ranged should never be on the melee aggro table unless it is their only option.
8: Use raid marks for kill order/CC. If you do not do this, your aggro issues are at least partially your fault.
9: If people refuse to cooperate with you, remove them from the group. There is no reason to tolerate such people. Raiding is a team effort, and people who do not want to be part of that effort have no place in a raid.
10: Never take responsibility for other players' failures, especially when they try to blame it on your class. Comments such as, "We wouldn't have wiped if a paladin was tanking." are almost always attempts at shifting responsibility and should be shown for what they are.
Sorry if I posted a lot of information that has already been posted or if any of my information/suggestions are in error. I am always open to constructive criticism.
@ previous
Sometimes it is, sometimes it isn't. An MT in a raid will probably get very limited use out of it, while a tank might find it a godsend in a five-man. Most of the time, it isn't needed, but it can make your life just that much easier.