Low level changes:
Those of you who have been considering starting a new rogue, I would caution you to wait until patch 3.3 if you really want to streamline the process. Blizzard is making the leveling period of 1-10 much, much easier, and they're starting rogues out with weapons in both hands right out of the gate: a dual-wielding death dealer. In addition, Stealth is being reduced to a single rank (in prep for Cataclysm) which reduces your speed while Stealthed to 70% of normal. Chalk up a 20% boost to Stealthed speed and greatly improved damage and health regeneration, all starting at level 1, and it's clear that the devs goal is to make starting a new rogue as accessible as possible. For more tips on leveling your rogue, check out Encrypted Text's guide to rogue leveling.
Preparation is also seeing a tweak, with its CD being lowered from 10 minutes to 8 minutes. This is due to the new Arena policy of "no 10 minute cooldowns", and Cataclysm's removal of all of the 'long CDs' from each class. They adjusted Filthy Tricks accordingly (from a 5 minute reduction to a 3 minute reduction), as 3 minute Preparations would be slightly overpowered.
Deadly Poison's dirty little secret:
Deadly Poison is the only pure stacking DoT in World of Warcraft, at least at the moment. While there are a few stacking DoTs, like a druid's Lacerate, Deadly Poison is the only one that doesn't include some sort of base effect outside of the DoT. If you Lacerate when you already have a 5 stack on your target, they take some amount of damage instantly, in addition to refreshing the effect. If you proc Deadly Poison when you're already at 5 stacks? Nothing but a stack refresh and a nice pat on the back for being a good rogue and remembering to use the right poisons.
In order for Deadly Poison's effect to be truly maximized, you don't want to 'waste' poison procs constantly refreshing it. Imagine if you could turn those extra Deadly Poison procs, when there's plenty of time left on your DP stack, into some sort of instant damage. Now you're gaining a ton of extra poison DPS, because you're essentially weaving those instant poison procs in with occasional DP procs to keep the stack maintained. There are so many wasted DP procs, especially now that Mutilate's favorite finisher, Envenom, doesn't consume the stack anymore. So why are we wasting so many poison procs for absolutely no gain?
In comes Adrine, addon author extraordinaire, with a shiny new mod: PoisonSwapper. A simple mod designed to automatically switch your offhand weapon (and therefor, poison) while in combat. It can detect your poison stack and the time remaining on it, and swap to a secondary offhand with Wound or Instant Poison on it when your DP stack is safely ticking away. Due to Blizzard not restricting the automatic swapping of items in combat, the entire addon is scripted and doesn't require any input on your end. If your DP stack is at 5 with plenty of time left, your backup OH swaps in and starts procing Instant or Wound Poison for you. Once the stack gets low, it swaps back until you get a Deadly Poison refresh, and then the process repeats itself.
The addon took the forums and community by storm, and with claims of triple-digit DPS gains, there was no reason NOT to be using the mod. It was advertised as "free DPS" and it truly was, but it also raised a concern that there was now a 'required' addon involved with playing a rogue in PvE. The issue is not with the addon itself, but with DP's poor scaling when the rogue is at the poison hit cap with growing haste values. Adrine found a way around that limitation, and it opened Blizzard's eyes to the problem underneath.
Mutilate had already seen a significant buff via a Murder change to make it affect all targets. Murder was often the 4% margin of difference between Combat and Mutilate on many fights, and setting it to 4% against all targets pushed Mutilate into a truly solid raiding build for any environment. This latest change that Blizzard implemented to fix the Deadly Poison problem showed up like a Christmas present on December 26th for Assassination rogues everywhere.
The fix for Deadly Poison:
Let's start off with adding 10% to Deadly Poison's proc rate by doubling the effect of Improved Poisons (from 10% to 20%). Alone, this change would be a slap in the face to those who complained about DP's broken state, as MORE waste procs would only compound the problem. The game-changer for DP comes from the second change, to Deadly Poison's base tooltip:
Deadly Poison: In addition to its existing effects, when a rogue applies Deadly Poison to a target which has already reached the maximum number of applications, this will also trigger the poison which the rogue is using on his or her other weapon.
In other words, if you have a 5-stack of Deadly Poison on your target, and Deadly Poison procs again, it actually procs the poison on your other hand instead. Assuming that you'd be using the PoisonSwapper mod to swap to the same poison as your main hand (since there is only one 'best' instant-type poison for each spec), this performs essentially the same function without the addon. You don't have to run an addon for it to work, you don't lose a GCD when the addon makes the swap, and Deadly Poison stacks faster in all situations.
Previously, a Mutilate rogue could count on Instant Poison having around a 40% proc rate on their main hand, and a constant 5 stack of Deadly Poison on their 1.4 speed offhands. Now that Improved Poisons will bring Deadly Poison's proc rate up to 50% (DP is not a PPM poison!), that means that your offhand weapon will be proc'ing your Main Hand's Instant Poison at a 50% chance every 1.4 seconds, meaning that your offhand will be doing more poison damage than both of your hands combined used to do. Unless Blizzard changes DP to be a PPM before then, Mutilate will demand the quickest OH possible in every situation and will blow every other DPS spec out of the water.
With Mutilate's poison damage spiking and Murder's new species agnosticism, Assassination has been absolutely destroying every other spec, build, and class on the PTR. Either Deadly Poison needs to be switched to PPM, or the MH poison proc it causes needs to be at half damage, or some other nerf to bring Mutilate back into the realm of every other class. Once properly tuned, Mutilate and Combat will be able to truly compete on any fight, regardless of mob type. The more that different rogue specs compete, the stronger and more balanced we will become as a class.