Another cool stat you'll need to read up on is mastery. Each spec gets a different benefit from mastery, which means that not all specs benefit from it equally. Affliction warlocks get Potent Afflictions, which increases DoT damage by a base amount and for each point of mastery; demonologists get Master Demonologist, which increases their demons' damage, as well as damage dealt during Metamorphosis; and finally, destruction warlocks get Fiery Apocalypse, which increases fire damage. Each of those base increases have different values, so there's a lot of fuzzy math when it comes to how much each spec benefits from mastery. Some specs will benefit from it more than other stats, but the general idea is that it demands a very specific type of playstyle for you to feel its effects.
There's also a lot that has been made about reforging your items for mastery. Understand that this is a temporary measure, because it's basically the only way to get mastery on your gear before Cataclysm. When the expansion hits, mastery will be natively found on level 85 gear, and maybe even before then. Mastery has pretty much the same stat weight as haste in 4.0.1 for warlocks, which is why it's important to reforge for it. Numbers are likely to change in the new endgame, so what's important for now is to get a feel for how mastery benefits your spec. The priorities for gemming, enchanting, and reforging will become clearer as the actual numbers come in through the expansion.
Warlock rotations have changed in Cataclysm to be more of a priority-based system rather than a set list of spells that you cast in sequence. I went over this a few weeks ago, but you'll still need to run those spells yourself on a target dummy to figure out your priority, especially when it comes to the those spells lower on the chain where the difference in DPS is marginal and can change depending on gear values, glyphs, or other factors.
You should also know that your spellcasting now will change quite a bit in Cataclysm because you'll be getting new spells to add to the mix. At level 81, you'll pick up Fel Flame, an aptly green-colored instant-cast, direct damage spell that has the further complicating effect of extending the duration of Immolate and Unstable Affliction. There are two notable things here. The first is that the spell is instant, which means it takes one GCD to insert into repertoire. The numbers are low, so it won't be part of a regular rotation, but since it's usable while moving, it is great for the many mobile fights you'll experience in Cataclysm as well as PvP. Second, it extends the duration of key DoTs with cast times, which makes it a great pinch-hitting DoT extender to buy you time to cast the actual DoT. This means it takes awareness to use Fel Flame properly and that you should be ready to adjust your priorities at a moment's notice.
At level 83, you learn Dark Intent, a unique spell that grants haste among other effects. To make best use of the spell, your haste should be at a point that casting the spell will push you over the next threshold so you can gain that additional tick. It's a curious spell because it's a buff you apply on an ally, increasing his DoT or HoT effectiveness. This means prime targets for the buff are shadow priests, feral and moonkin druids, and maybe unholy death knights. This changes class synergies and makes your DPS reliant on another team member. This changes the way you approach your DPS -- you'll need to look for a proper target who will scale right along with you. You should also note that it's a buff. Warlocks actually get a buffing spell in the expansion. I know -- weird, right?
Finally, at level 85, you'll get Demon Soul, a long-cooldown spell that grants different effects based on the demon you have summoned at the time of casting. While succubi are the higher-DPS demons for affliction warlocks at the moment, Demon Soul might actually propel felhounds back into the fore. We'll know for sure when the numbers get crunched. This is a spell that needs to be activated every time it's off cooldown for optimal DPS, and it should be noted that its duration varies depending on your active demon. This means a whole lot of new numbers for your spell rotations come Cataclysm. Whatever spell priority list you have now will be affected in the expansion, so don't get too comfortable.
While it's entirely possible to play your warlock without external help -- certainly Blizzard has made it so that the narrow specializations of each tree guide each player to the spells they're supposed to cast -- getting to the top of the heap means a whole lot of reading, testing, and number crunching. DPS, as some players will tell you, is serious business. Personally, I think it's almost too much work. I don't hide my distaste for game math, which is why I grudgingly scour various forums and blogs for the numbers and do tests from there. The bad news is that no matter what class you play, you will actually need to study quite a bit to play the game well.
The good news is that there's a ton of reading material available, some more
Blood Pact is a weekly column detailing DoTs, demons and all the dastardly deeds done by warlocks. We'll steer you toward tip-top trinkets and Soulburning your way through Cataclysm.