good luck in arenas as holy. Holy is good (prolly even better) for non-rated bgs since you don't get focused as often but seriously good luck living through any zerg as holy, you just dont have those defensive heals and shields that you get as disc.
I used to love Disc for PvP but since Cata it seemed to lose something. Been playing Holy in unrated BGs and it still feels I get focused - pretty much always...people are just trained to go for the healer aren't they.
As for defense though - I find speedy shield invaluable for getting out of scapes (even without the new 4 piece bonus)...Guardian spirit, desperate prayer, chastise, cure poisons....it doesn't seem OP but it does seem that we now have the tools to not be a total target dummy.
Disc though? Seems a bit like the poor cousin. Maybe I'll respec tonight and give it a spin.