being that you have trouble reading, i'll point out that I felt it was the best and most viable spec for AQ40 (7-10-34 being the spec im talking about here). Note that 3 out of the 4 harder fights value burst damage much more than say a 2.5 second shadow bolt. For example, killing bugs in twin emps, you want burst dmg, so an immolate+conflag is gonna do more dmg than a single shadow bolt. In C'thun I know I loved conflag for killing tenticles. Finally in Visc, while warlocks have no real roll in this fight besides stay alive and have an imp out, conflag is definatly great for killing mini blobs. Aside from dmg you have demonic embrace (which i know kept me alive through some early emp pulls) and imp imp to benefit your group. I also had imp healthstone at the time cause i really had nowhere else to put the points.
now i'll definatly concede that SM/Ruin is w/o a doubt the best pure dmg spec for a warlock. I've been sm/ruin since naxx was released and know that if I was still conflag i wouldn't be able to keep up on dmg meters. W/ my current gear the highest I've come on damage meters on a Patchwerk kill is 7th, ahead of all our mages. one of our other warlocks has stayed conflag (w/ over 570+ dmg) in order to have a warlock in the raid w/ imp imp and he hasn't broken the top 15. The reasons for this are multiple but the most obvious is just strait up gear. As a conflag warlock you simply can't split dmg (except ofcoarse on your gloves which you have to), having any +fire/+shadow dmg items just hurts your overall dmg too much. Because you can't specialize in one area for dmg the best dmg set you can put together is like 600 and thats with the best gear in the game. Shadow dmg also happen to have some of the best itemization in the game and becuase of this aquiring 600+ shadow dmg is not terribly difficult. I rock 652 shadow damage with my current gear and have multiple slots i've been waiting to upgrade. As you said in your post conflag is horribly mana efficient and because of this in any sustained dps race, such as Patchwerk, the SM/ruin lock has a huge advantage because of syphon life, along w/ ofcoarse the +dmg modifiers from a 2.5 second cast time. All in all each spec has value, its just a shame blizz has managed to phase out fringe dmg specs for locks and hunters from any fight that doesnt need tranq.

While posting this, I only had fire mages in mind... -_-
But I can't believe I forgot the Destruction tree pretty much means "fire mage," and that most raiding warlocks are SM/Ruin specced.