not really.
I recently switched to a mainly disc build and so far I am loving it (43 right now), I can pull a couple mobs at a time without fear of dying, hell I accidentally got 4 adds yesterday in tanaris ... f'n pirates ... and survived just fine.
5/5 spirit tap and 2/2 in healing focus then the rest in disc is what I am using.
My fights consist of:
-PW:S on me
-Touch of weakness on me
Open with Holy Fire
SW:P
Smite
Wand til dead, maybe toss in another smite and refresh SW:P if needed.
I have basically 100% mana at the end of the fight and can just chain pull non stop.
I have no doubt that shadow will kill mobs faster but IMO you give up alot of survivability. I know the world screams shadow for leveling but just be aware other alternatives are feasable. I was a pain to kill in the BG's too and managed to top the healing meters on several WSG rounds.