Over my time playing WoW, I've encountered a lot of people who didn't really know anything about rogues, beyond that they are melee dps who can stealth and have Sap. Hell, I used to be one of those people. So I thought I'd do a quick primer on the most basic things one would need to understand to really "get" rogues from a raiding perspective.
Since rogues generally bring little utility to a raid, the only real metric to measure their performance is their damage done. This I mostly a function of damage per second, but is also influenced by their ability to stay below the tank in threat, and stay alive (dead rogue does no damage!).
So, in general, the strongest raiding rogue spec is the one that contributes the most damage to the raid.
Most of a rogue’s damage is “white damage” (regular weapon swings), so the strongest raid spec is one that boosts that damage the most. This is why builds that emphasize the Combat talent tree are generally the highest raid dps. The Combat tree also scales exceedingly well, especially with +hit and haste. This is mainly because of the talents "Dual Wield Specialization" and “Combat Potency”, which grants extra energy on a per-hit proc basis. So, the higher your hit, not only the higher your damage, but the more combat potency and poison procs you will shoot off. Since Combat Potency only effects the offhand, rogues want the fastest offhand they can get (1.4-1.6 speed). Meanwhile, their yellow attacks such as Sinister Strike, and their sword specialization, benefit from slower mainhand weapons, so they would want a mainhand with a 2.5-2.8 speed. Daggers require similar itemization, but the numbers are lower (roughly 1.3 speed offhand and 1.8 speed mainhand).
The Combat tree includes a set of 5-point weapon “specializations” that are very worthwhile. Thus, Combat specs are usually defined by which weapon type the rogue chooses to specialize in.
More after the break:
For raiding purposes, Elitist Jerks lists the various rogue specs in the following order, based on personal dps. All other specs list how much less dps they do than Combat Swords. I don't link to more than one Combat build because they are all pretty similar, and I'm just trying to give you the gist here. My example specs are not the "only" way to do each type of spec, there is definitely some space for personal preference with some of the talent points.
1. Combat Swords and Combat Fist+Swords
2. Combat Daggers, Fists, and Mace+Sword (1-2% less dps)
3. Combat Maces (3% less)
4. Tri-spec Hemo (5-6% less)
5. Shadowstep Hemo Raiding (9-10% less)
NOTE: Mutilate spec (deep in the Assassination Tree) cannot be properly modeled, but is estimated to be somewhere in the range of #4 or #5 for raid dps.
So why would anyone spec #4 or #5?
Because of Hemorrhage (Hemo). Hemo replaces the normal instant attack, Sinister Strike. It does roughly the same damage, but costs slightly less energy. Its real value is that it applies a debuff to the target. The debuff has 10 charges, and adds 42 damage to ANY physical attacks done to the target. This means that if the full debuff is consumed, every Hemo does an extra 420 damage. Most raids have enough physical damage being dealt at once that most of the charges are consumed almost immediately. Mathematically, Hemo is estimated to contribute about 100 dps to a raid. Please note that this DOES NOT SCALE with gear. A Sunwell-geared rogue with dual Warglaives will provide exactly the same Hemo debuff contribution as a rogue in blues: about 100 dps.
Build #5 is not recommended, since it does significantly less dps than other Hemo builds (#4). The only reason to consider it is if you are raiding with a tank who has low threat generation and you raid has no paladins, because it is the lowest-aggro build. All of the dps of the other builds goes to waste if you have to throttle your damage to keep below the tank on threat. But even then its usefulness is limited, so avoid it for almost all raiding situations.
All rogues deal dps in the same way: they spend energy on their primary combo-point generating attack (sinister strike, hemo, or backstab), then spend the combo points on finishers. Rogues get the highest dps by maximizing the uptime of their two best finishers: Slice ‘n Dice (increases attack speed) and Rupture (bleed effect). They do this via cycles. For instance, I’ve determined that my best dps cycle is to do a 1 or 2 combo point SnD, then a 5 combo point Rupture. In a tank and spank fight, this allows me to keep 100% SnD uptime and come damn close to 100% Rupture uptime as well, without any wasted energy.
Daggers specs, which can use backstab, have playstyles that feel very different from Sword/Mace/Fist and Hemo specs, which is why you will often see dagger rogues pass on swords that look like upgrades, and vice versa.
A Tri-spec Hemo build will often contribute the most dps to a raid, but there is a "point of inflection" where the raid contribution of Hemo is eclipsed by the extra personal dps that could be gained by switching to full Combat. This point is when the Rogue is wearing mostly tier-5 level gear. So you will never see a Hemo build in Black Temple or the Sunwell, though it can be a very good build for Karazhan. Please also note that you should only have, at most, ONE Hemo rogue in a raid. The debuffs do not stack from separate rogues.
Aside from the rest of the spec, it’s generally agreed that all raiding rogues should have at least 11 points in the Assassination tree (these are the points). Those points are key raiding talents for keeping up a good cycle and preventing rage starvation, particularly Relentless Strikes.
So now you know everything you need to know to grasp the basics of rogue raid dps, converse relatively knowledgeably about it, and not get confused when your favorite rogue does something that looks wierd. Maybe it will even help you catch when your least-favorite rogue is messing up.