The obvious use for Smoke Bomb is to defend ourselves and our party from hostile attackers by dropping the cloud and hiding inside. I see this as particularly useful for protecting a healer caught out in the open in an arena or battleground. They'll be immune to both direct damage abilities as well as Silence and Counterspell, since they can't be targeted while inside. By allowing our healer to spend some quality time healing without being molested by ranged attackers, we can prevent a positioning mistake from turning into a loss. Similarly, we could shroud one of our friendly ranged attackers to give them free time to unload their most powerful spells without fear of being focus-fired. In addition, our teammates can use any techniques that would normally leave them vulnerable, like Evocation or resurrecting a pet.
If we're getting blown up and Combat Readiness is already on cooldown, we can fall back on Smoke Bomb to provide us with a few moments of peace against ranged attackers. Sure, they can use their AoE abilities to damage us in the cloud, but there's a reason they don't use those AoEs already; they're weaker than single-target damage, and they cost a ton of mana. The opportunity cost of using an AoE attack is a benefit in itself, as we're causing our opponents to use a high-risk technique to simply do average damage to us. If they choose to save their mana instead, we could use a Smoke Bomb to restealth and then start a fight over.
The offensive push is where Smoke Bomb can really shine -- well, as much as a cloud of debris and dark smoke can shine, that is. Imagine that a frost mage is attempting to kite you or that you're knocked away from a boomkin by Typhoon. You can drop a Smoke Bomb between yourself and your prey that will allow you to charge at them without fear of being rooted or Frostbolted. You can use it to advance your entire team's position in an arena, dropping it between pillars to allow you to migrate around the room. By preventing your team from being snared or attacked, you buy yourself time to close the gap between you and your opponents and then eviscerate them from close range. It also gives your healer time to top off the group as you move forward, which means that you're ready to attack when you reach your prey.
The fun doesn't need to stop once you've reached your opponent, though. While we don't yet know if Smoke Bomb's effect will prevent enemy healers from targeting their own teammates inside the Smoke Bomb, I believe that it will. Imagine throwing a Smoke Bomb onto a wounded healer, preventing any of his teammates from Intervening or using a crowd control effect on you as you execute them silently. It could be used to prolong the amount of time a target goes without heals, by isolating your foe from their healer while waiting for diminishing returns to become active. I imagine an AoE cleave of my own: Smoke Bomb a group of enemies surrounding a flag and focus all of my party's AoE effects onto the cloud, while their healers stand back in horror as their Grid goes from green to yellow to red.
Do you remember Cyclone, the ability that defined arena play in BC? While Cyclone wasn't exactly a potent CC when compared to Polymorph or Fear, it had one advantage that no other CC had: It prevented healing and buffing done to its target. If Smoke Bomb shares this property, we may have the ultimate arena ability. It's like having a surprise pillar in our pocket that we can deploy to ruin even the best laid plans of our enemies. I can only imagine the fear in a priest's heart when he sees himself trapped in a dark cloud with two rogues, his teammate unable to assist him in any way without compromising himself. Shadowstep and Smoke Bomb will have an immense synergy, with our ability to remove an enemy player from the field at any time.
I think this is an ability with potential in PvE play, though I'm not quite certain on what types of attacks it will work on. If we could drop the cloud on the melee group on a fight like Lady Deathwhisper, where there's plenty of Frostbolt Volleys going around, we could reduce our incoming damage by an appreciable amount. The problem is that too many effects are AoE-based, which means Smoke Bomb won't be effective at all. How often does a rogue get targeted by a single-target ability in a PvE encounter? I can only think of a situation where there are caster adds, but tanks usually handle that rather quickly.
I do see it being useful in something more like a 5-man dungeon, where we can drop a Smoke Bomb, have the entire party get inside and then have the tank pull the ranged enemies. This would be a godsend in an instance like Halls of Reflection, where many players are stuck abusing a small corner of the wall to break line of sight with the mages and hunters. Smoke Bomb will definitely make a tank's life easier in PvE, though I don't see it being very useful in a raid situation. That's fine with me, as I believe its PvP potential more than makes up for that deficit.
Who knows? Maybe we'll be able to use Smoke Bomb to become immune to some attacks, like we currently rely on Vanish to do when we can. Let me channel Ming here for a second: "As long as warlocks don't gain the Sharingan Eye ability to pierce the dark cloud of our chakra, our Smoke Bomb should hold up against their most powerful jutsus! I predict the new 'Neilyo move' will be Smoke Bombing a Death Coil! Believe it!"