Listen, for PvP there's no secret. It's a very mediocre spec with little pay off for its worth. Unless, of course, you enjoy tab dotting and bolstering your ego across the scoreboards over useless damage numbers - go for it. As far as killing and control power goes, there are other specs that outclass it in every way imaginable.
I personally look at the buffs and my character lighting up for the proc.
It has a steep learning curve, but as I said before - barely worth it. It's a lot different vs a Watchman sent, who, by all means: pays off quite well for its ramp up.
Not to disagree to much, but its not terrible for pvp. I find that creeping terror is solid addition. I think its very good against LOS healers like operatives to keep pressure on them. I find that DoT's have an added benefit to pvp and that is making the healer work harder. Especially now that almost everyone runs a burst pvp spec its not bad to have a DoT specced player with solid burst on a team. I like it with stealth. I find it helps against teams with skilled players (healers) that are effective. First is they see damage ticking. They may be not healing the right target once your burst players start spiking someone. Meanwhile they have to switch to the guy getting targeted and your 5k dots are still ticking or need to be cleansed.
Against these massive bubble spec teams its always good to try and pop bubbles at range. Madness is good right now if only because it changes your engagement style to open ranged dot, then close to kill. It has 2 long range attacks that hit for internal damage. It gets a fairly good amount of healing going if you dot up the enemy team.
It's weakness is the softness. Your not going to want to go head on against other burst players. You want to harass and flee. Its more of a dps support class. While I agree on its burst lacking the power running it as an assassin can actually produce more wins in pugs than people realize.
Its ok for huttball. Instant Whirlwind and creeping terror are good skills there to go along with improved force speed and more CC breakers per match with advoidance from deception.
One of my favorite tactics. Sitting by the friendly back row. Dot up some people. Watch your melee dps close. Creeping terror the target. Most healers are seeing smash or ravage coming and they are using that aoe cc. One you see that you charge in. Proc up your melee. Slow them. It can really help to kill those healers faster. Meanwhile that off healer is busy working your dot damage and other damage coming at the group.
What doesn't work is a team of all DoT spec players. Mixing in Madness with smash is very nice. IMO.