sl/sl is a survivability and control spec. you have the damage mitigation and life return to keep going for a long time, while also being free to control one or two people depending on the situation.
in 2's and 3's its mostly an outlast spec. in 5's its mostly a control spec. in bgs its fairly strong, and your ability to deal damage and survive increases as your opponents grow more numerous. with a good healer by your side you can tank quite a few people. the best ive seen to date was a friend of mine in eots, with the flag, at fel reaver ruins. he had a disc priest and holy paladin with him, and they went up against 9-10 horde. the battleground ended before he died, a good 8 minutes after he first charged the place. the horde just couldnt bring him down.
knowledge of when to sac a voidwalker is key to lasting thru the worst your enemy can throw at you.
the major weakness of this spec is priests. theyll dispel everything if theyre smart, and tab-dotting is a great way to make prom an ultra-efficient heal. a good priest will force an sl/sl lock to do more single target damage, something the sl/sl doesnt specialize in. in smaller group situations, the sl/sl is best served by draining the priest of mana before loading up the dots. in larger situations, having someone apply more direct pressure to the priest can give you room to dot up the priest and an additional target, increasing your dps and incoming health by a decent amount while also limiting the likelihood that prom will bounce around like a five year old on a sugar high.
as for pve, sl/sl usually wont top damage charts, but they do make premier seeders, because no other aoe class can put out the damage a seeding warlock can, and no other warlock spec can handle incoming damage like an sl/sl can. my only experience is with the 10-man instances, but there are a number of times having a smart sl/sl lock has taken a fight from "tough" to "easily manageable". with VW talents the blueberry becomes a decent off-tank on situations such as moroes or malacrass, building damage-less aggro thru manual taunting so that when the CC breaks they mobs go for the VW instead of the healers.
the life return and general control/survivability aspects of an sl/sl lock give it tank-like attributes in some situations as well. an sl/sl lock can, with fel hunter out, continue to do full dps during phase 3 zul'jin, hastening the completion of that phase.
finally, a good sl/sl lock can easily CC two mobs at once by using yo-yo fearing and VW tanking at the same time. instant cast dots mean the lock can still maintain some dps on the main target while CCing the other mobs, and soul link gives the lock the breathing room necessary to deal with the odd resist or early random aoe. their ability to self-heal is also great for healers, essentially giving the healer one less target to worry about.
Edited, Mar 19th 2008 5:21am by Quor