Ask and you shall receive!
At 70
PvP Arena: SL/SL is great, you might think about taking Shadow Mastery in the Affliction tree instead of "Protect my pet for 1 sec longer". Also, Demonic Resilience lowers the chance to be crit THREE less times out of one-hundred crits, WOW, useless. Shadow Mastery will also give you about 100 spell dmg more than Demonic Knowledge. SL/SL is probably also the best farming spec. Be aware that some Arena teams need other specs for utility, some need UA. Be willing to try different things to make your rating go up, while finding what works best with the classes you play with and the size team you're on. SL/SL will perform sub-par dps in instances and raids.
PvP Battlegrounds: Felguard with Destruction. I take Shadowburn and Destructive Reach. It owns, especially with the trinket from Tempest Keep. However, you can roll SL/SL in BG's and melt faces just as well or better, it's a different playstyle though.
Raiding - Low Spell +Hit: Affliction with UA. If you have low spell hit, you probably have low spell damage as well, take UA.
Raiding - High Spell +Hit: Affliction with Ruin. Simply does more damage than UA if you have crafted or Kara epics. Still, a good Warlock can out dps the rest of the raid with UA but if you want to be all pew pew and shit...
Raiding - Monster Spell Damage: Performs the best at hit cap (202 +spell hit). Basically you go down to Shadow and Flame in the Destro tree and Demonic Sacrifice in the Demo tree. Stay away from talents that appear to be PvP oriented. Sac the Succubus for the highest dps in the game. With the correct gear, sac the Imp for the highest dps in the game. While farming, sac the Felhunter. If you're in BEM doing dailies, sac the Voidwalker. Great farming spec, not as good as sl/sl. Probably not raid worthy under 17% crit (without any Destro or Demo talents) AND around 150 spell hit. You must put all three points into backlash. You can do all the fire spells or go for more mana for a pure shadow spec with Cataclysm. Imp Searing Pain is really for Warlock tanking only.
While Leveling
Affliction for the lower lvl's. Learn how to keybind, and what it means. Do not click with a mouse to cast ANY spell, do not roll a Warlock if you can't do this. Affliction provides ways to more efficiently grind without as much eating and drinking, THUS, cheaper, by far.
In the mid-lvl's do a hybrid affliction/demo/destruction if you're on a pvp server to get fast Shadowbolts, Insta Corruption, and max out points in Improved Succubus talents.
In the mid-lvl's if you're on a PvE server, continue down the Affliction tree, picking up Dark Pact. Super mana efficient, enjoy not having to buy hardly any food or water.
At lvl 50, pickup the Felguard, go solo for your Infernal. At this point you can go back to Affliction or stay with the Felguard while putting points back into Affliction. Make sure you take the talents to instant summon a new pet, don't take points to buff the Voidwalker or Succubus if you're speccing the Felguard.
At lvl 60, you can take the points back out of Affliction and go with the fast Shadowbolt and continue with talents that buff Destruction (Reach), and my Destro must have (Shadowburn). Or you can wait till lvl 61, and get Siphon Life and Soul Link (SL/SL). If you haven't played SL/SL before, I'd recommend trying it first. Also, if you're on a PvP server, I'd take SL/SL, hands down.
Raiding No-No's: Don't show up to Raids with PvP talents. We don't want to wipe on new content because you're too lazy to spend 50g to respec.
Popular crappy talents in raids:
Fel Concentration - You're an idiot.
Curse of Exhaustion - You can do Vashj and Hyjal w/o it.
Howl of Terror - Are you fracking serious.
Felguard - It's possible, but nobody wants to see it.
Shadowfury - I love stomping these people.
Ok, so now any mob, five lvl's over you should be in your reach. If this isn't possible for you, and you followed the above suggestions, check the gear. You want Stam, Int, and Spell Damage. Spell Damage above all else, I know there's a lot of Spirit stuff while lvling. Please, please, please, help yourself and try to stay away from it if you can. Sometimes it can't be avoided. Don't be scared to keep wearing something that looks like it has the right stats over something 20 lvl's later that has crap on it. Like nuking your spell dmg for spirit with the same stam and int. Forget that.