A well timed curse is a warlocks best friend. It's instant. It's usually low mana and it can serve lots of different functions.
Curse of Agony/Improved Curse of Agony: Damage DoT. Not so useful for things that die quickly, since it ramps up damage towards the end of the curse. Amazingly useful for long lived mobs. If you have three warlocks in the group, the lock that has Improved Curse of Agony but not Malediction should be doing this one, leaving CoE and CoS to the Malediction or non-Improved CoA warlocks.
Curse of Weakness: Useful for those mobs that hit like Optimus Prime. Heroic bog lords in Underbog come to mind. It does not stack with other CoW's from other warlocks, so pick one warlock to do this and stick to him (best if it's improved curse of weakness). In general, not often used on bosses when CoS, CoA or CoE is far more useful in raids, unless you have an unheard of four warlocks in one raid group.
Curse of Recklessness: The best use I've seen for this is when you're fearing something but don't want it to go too far. Swap between CoR and CoW. CoR will bring it running back to you. CoW sends it running away again. (or any other curse, really.) I've also heard in PvP if you use it on a warrior who throws up spell reflect, you've suddenly become immune to fear.
Curse of Exhaustion: I don't have this one myself. It's a talent, not a purchased skill. Makes them run away slower.. or chase you slower. Whichever is more applicable to your situation at the time. Need to kite something? This is your baby.
Curse of Shadows: If you're in a raid group with multiple warlocks OR shadow priests, this is the curse of choice. A warlock with malediction should cast this over a warlock without malediction. Get together with your raid warlocks and figure out who has what curses improved.
Curse of Elements: If you have a mage in your group, this is your curse of choice. Again, Malediction Lock> Non Malediction Lock.
Curse of Doom: Useful for various bosses, the Curator being one that comes to mind instantly. Another one where it's useful is the end boss in ZA. He eventually becomes a form that, whenever magic is cast AT ALL, it damages the caster. If you slap a CoD on him about a minute before he transforms into the hawk form, and then try to keep that up whilst wanding, it works nicely.
Curse of Tongues: Used on various casting mobs. Increases casting time. It's used on a few boss fights and trash pulls in 25 man raids. Again, only one of these can be on a mob at the same time. So assign it to a particular warlock.
Amplify Curse is a affliction lock talent. I'm not 100% sure if it works with the CoS or CoE or any of those, but I KNOW it works like a lovely lovely charm with CoD on the Curator and also improves the damage output of CoA.
In general, CoE and CoS should be put up for anything -- trash mobs, etc, if there is a mage or shadow priest in the group. If you have 1 lock, 1 mage and 1 spriest, CoS is the way to go. If it's just a lock and a mage, pick whichever of them will boost the better DPSer.
5 points in the affliction tree will make your Corruption spell instant cast.
Did you hear me?
Why wouldn't you get it?