From my testing on the PTR, though admittedly not 100% scientific, I actually saw more use out of glyph of vendetta (remade out of hunger for blood so most of us should have it) then backstab.
As the majority of my test was on the dummy though I cant say for certain of course till I get into static raid comps on a boss to compare. I also saw more use in picking up deadened nerves for filler points, simply because the less damage you take the more likely you are to not die if a healer has to choose between you or a more important raid member.
Something else of note, on the ptr I found reforging as much hit as I could into mastery increased my overall damage output as long as I stayed above hit cap, in my current gear I had enough to reforge every piece of hit I could into mastery netting me a 30% bonus to poison damage give or take, a huge boost bringing my instant poison far ahead of my next highest damage source.
Last I logged in on the ptr I was using a spec of
Talent Calculator - World of Warcraft with a rotation of 3+ rupture 4+ envenom, though once servers come up I may replace the rupture glyph with something else.