I've been leveling an Operative, and been playing as Lethality. I'm up to level 33 now. I'm finding it interesting and it has some great advantages in PvP (stun on 30s cooldown + movement buff, AE snare on CG), but it's quite difficult to play this spec, partly because the rotation is weird, partly because the energy requirements are so severe. It's almost like playing my Pyro Powertech, because I'm usually in the red zone. That's fine in PvP where you don't expect to live long after you Shiv and Cull the healer, but in flashpoints, I can't find the right balance.
I feel like I should be taking some of these extra damage abilities off my bar if they're too expensive to use, but I'm not sure which ones. Backstab is useful instant damage for 10 energy. Overload Shot is buffed by my AC and by Lethality tree. Should I leave out Carbine Burst, seeing how it consumes a much-needed TA and isn't as good as Cull? I rarely use Snipe or Explosive Probe in this spec, but they're on my cover bar only anyway.