A couple of things I would note about the differences between normally-geared (i.e.: if you're in full raid epix, STFU and go farm something, noob) hunters and locks at 80.
  • Warlock's Health Funnel heals for more than mend pet plus it reduces damage taken by the pet by 30% while active, which is HUGE during an enrage or whirlwind, etc.
  • Voidwalkers can tank hard elites even while specced mostly affliction, whereas hunters must spec BM to effectively tank a hard elite for any length of time without kiting and pulling aggro every 3rd shot. Which means your lock's DoTs are doing excellent damage, your drain life/siphon life are healing you very well and your mana/health basically never drop enough to worry about.
  • Warlock's have effectively infinite mana while not having to reduce DPS as affliction.
  • Hunter pets do a better job of AoE aggro control, though neither is anywhere near a consecrate or thunderclap/whirlwind tank.
  • Warlocks don't spend money on ammo.
  • Warlock CC isn't as friendly in small spaces with close aggro, whereas freezing trap is.
  • Soulstone x4 > jumper cables. Period.
  • Warlock AoE is honest AoE, whereas nerfed Volley isn't all that hot. (Also, see infinite mana above)
  • Warlocks can DoT on the run and facing away from the target, which means after a fear, you can re-dot the mob/boss and THEN round everyone up while the VWs are tanking it.
Having said all that, most of my 80 experience with them is solo/duo, not multiboxed. But you can extrapolate how well the pets will survive based on this if you think about it a bit. There are some folks who've been blowing up instances AoE and it's hella fun and looks cool, but it doesn't scale. Try that in a heroic and you get eaten. What's the old saw? Slow and steady wins the race (with obvious caveats about certain boss's enrage timers).

http://www.wowhead.com/?talent#IdxMbhbAoVVMbkZ0GfbkAdm

That's my lock's spec. He's been able to solo all but the really difficult 5-man stuff in Icecrown with the void and was able to easily duo all of the 5-man stuff with my druid (except Alumeth). Put 4 of 'em together with a healer class and things just die.