if it does more dmg and you are willing to pay the price in mana.
I totally agree with the mana concern, especially since it costs more than twice the cost of steady. Anyways, this discussion prompted me to take some screenshots of my current shots damage and mana cost and some interesting conclusions came out of it, I'm including them below. Also Serpent sting is THE WORST shot you can use as BM.
(note: all tooltips were shot without buffs, except for Aspect of the Hawk - 155 bonus AP)
So here we have all the shots a BM hunter can use in a 1:1 rotation. They all have casting speed lower than the GCD, and we can only fit one of them between two auto shots if we dont want to clip the autoshots in question. As I see it, with my AP and base weapon dmg, coupled with about 600 armor ignore, there's no more point for me to use Arcane shot. Have to do some more testing on bosses, but I think even the fact that physical dmg is affected by armor wont make that much of an impact (bosses are debuffed, armor ignore, etc). Multi-shot however seems the shot to use on cooldown instead of steady, if you have no mana issues and no CC targets are in the vicinity of the taget. From my experience as a BM hunter (thats the only spec I've raided with, except for 1-2 kara runs as Marksman, didnt like it) Mana really isn't an issue past the middle of SSC. With mana oil on your weapon (or your two weapons for greater effect), Mageblood elixir and Blessing of Wisdom, you should have no problem at all for fights shorter than 6-7 minutes, even without switching to Aspect of The Viper. Proper potion use is key of course. Thats not considering Judgement of Wisdom on the target which if present is something amazing, as your auto-shots also return 75 mana per hit, also there is the Efficiency talent if you cant handle it, although Improved hunter's mark directly affects your pet dps, not to mention the whole raid's physical dmg. Also there are Darkrunes, Demonic runes, those little plants from Felwood, Alchemist's stones which are upgrade-able in the next patch, etc. (I won't mention a shadowpriest, cuz I'd rather be with the physical grp if possible, durid 5% crit = yum. )
Ok, I drifted off a bit. About the Serpent sting: You probably see yourself that it is utter crap. It certainly has use in a marksman's or survivalist's shot rotation, as you can add it after a steady if your arcane and multy are on cooldown. But for BM, let's make a little comparison between serpent's sting and the least impressive shot on that picture:
Let's say raidbuffed i get 5% more crit on average, making it to 30%. (27%-33% usualy, depending on paladins, druids, shamans and etc)
I won't bother adding any AP from raidbuffs, as they both scale with AP and even if there was a difference it would be minor enough not to affect final results of this comparison:
Serpent sting: 842 dmg. That's all you get. No crit. Average SS = 842
Arcane shot: 546+30%1256=546+376.8=922.8 (~923) Average AS = 923
(plus, your crit enables a Kill Command, and also makes your pet gain 50 focus for more claws, bites etc)
Not to mention the STAGGERING mana cost of Serpent Sting, equal only to Multy-shot.
And the nature of the 1:1 shot rotation does not allow more than one special shot be fired between two autoshots. In conclusion:
Using Serpent's sting is basically equal to shooting yourself in the foot for a Beastmaster. If you feel you have to use a sting, keep Scorpid Sting on the boss. Not sure if 5% less hit is any help to the guy tanking, but I like to think so
Anyways thats just my thoughts on the subject, I may have overlooked something, so if you disagree or want to point out errors in my observation, by all means, go ahead
P.S.
And yea, obviously arcane shot is not as good as I thought it to be, it was an adequate alternative with worse gear tho, apparently steady shot scales better :>