sap is an excellent tool, with a range greater than the radius of aoe abilities. In arenas a good rogue can easily sap a dh while they are darksighting by hiding behind a pillar and popping out with a shadowstep+sap.
You can tell how much time is left on a flare by how far the center of it is from hitting the ground.
Paladin/warrior aoe is really short ranged, just keep your distance, and you can predict pretty reliably where a dk is going to drop DnD, and you can even sap a warrior mid heroic leap and they wont do damage on landing.
Distract can change the direction a player is facing, its really disrupting (have fun watching people run off cliffs when you toss your distract)
Subterfuge talent used to keep you invisible for 3 seconds after taking damage, it was… unfair. Evis->mfd+evis-> ambush+vanish killed so many under-geared players in MoP (fire-watcher anyone?).
And they wouldn’t even know what killed them without checking their combat logs to see it was a rogue