Cataclysm has changed tanking a bit. Face roll is no longer allowed. You can still AOE tank just fine, but the amount of damage you take is nearly unmanageable. You need to be well prepared and use the tools that you have available. And yes, DPS are tools....in more ways than one :P
Rule number one of Tank Club: Mark your targets. Marking your targets is amazingly easy. I bound the symbols to my number keys for quick marking. It also makes it easy to mark on the fly. Make sure that your DPS knows what each mark means. Skull is first kill, X is second, Sheep the moon, Sap the Star etc. etc. If the DPS knows what the marks are there for, they are a lot less likely to CC something that you don't want CCed.
Rule number two of Tank Club: Take advantage of the CC that you have available. Ask the DPS to use it. If they refuse, then just boot them. If they are not willing to help you be successful, they don't need to be there. The best forms of CC are the ones that last. One of my favorites is Mind Control. You can have a Priest Mind control a mob and have it work on killing another mob. This is essentially a double CC method.
Rule number three of Tank Club: Don't break the CC. The CC is important. It makes it easier for everyone involved. Don't break it unless you mean to. Be careful with your AOE. Make sure to pull the other mobs back so that you are not in danger of breaking the CC before the duration is up or you are ready for it.
Rule number 4 of Tank Club: You have cooldowns, use them. As a tank, you receive a nice number of defensive cooldowns. I use shield block whenever it is up. I use my shield wall or last stand when it looks like the healer is having some problems. Be proactive with your cooldowns. Shield wall is not a 30 minute cooldown like it was back in the day. Don't be afraid to use it on tough trash pulls. Also for Warrior's spell reflect is a thing of beauty. You take no damage, and your enemy does. Use it every chance you can against caster mobs.
Rule number 5 of Tank Club: Interrupt. This doesn't just go for tanks. This goes for DPS as well. Interrupts are very important and will not cause a substantial loss of DPS. Interrupting can even make the fights go by that much faster. If nobody is interrupting the heals, then it is going to take a long time to finish the fight and there is a greater likelyhood of a wipe. Stuns are nice. When your target is stunned, it does no damage. That could be considered a defensive cooldown in itself.
Rule number 6 of Tank Club: Kill the Caster first. The casters are often times the biggest pains. They don't like to come to you and they easily aggro on your healer if you don't get a good handle on them from the get go. They may be healing or they may be shadow bolting your face off. Either way is not good, especially as armor does not mitigate spell damage. If you are a warrior and specced into gag order, Heroic Throw is perfect for pulling them. Or you could use the next rule......
Rule number 7 of Tank Club: Line of Sight Pull. LOS is nothing new. And it still works. If something can't see you, it can't hit you. This is perfect for getting that casting mob into range if you don't have another way.
Rule number 8 of Tank Club: Watch that PAT. Patrols are dangerous in Cataclysm. One Patrol has the potential to pull several other mobs and be the difference between a wipe and success. Make sure you are pulling back when needed and don't take on too much at one time. If a trash mob is by itself, there is a reason for it. It is gonna hit you hard. Be kind to your healer and pay attention.
Rule number 8 of Tank Club: You DO talk about Tank Club. The best sources of knowledge for tank are other tanks. Maybe a tank has a better way of doing something. Maybe they know a different strategy. There are a lot of things you can learn from other tanks. You just have to be open to it. Every tank has room for improvement. Don't be THAT GUY.
Following these rules and a little help from your friends should make your instance experience a much better one.