So a while back I asked about whether discipline spec was a viable option as a healer. And thanks to the latest talent tree specs, I strongly believe discipline is the way to go for healing. I tested the heals on both specs and the difference wasn't enough to convince me holy was a better spec for healing anymore. Although holy spec gave me bigger heals (greater heal about 4700hp average holy spec and 4200 average discipline spec) discipline gave me penance and spell haste. Penance I must say is the ultimate heal. Its instant, 3 1500hp heals over 1.5 seconds (4500 hp heal if at least one of the heals doesn't crit) not to mention divine aegis. I never run out of mana also.
I've healed kara, Hyjal, and nearly every heroic with no issues whatsoever. I've found discipline spec gives the healer enormous flexibility when it comes to on the fly heals, mana consumption, and survival. Of course having a good group helps also. I've been in groups where I just sat back and let prayer of mending do all the work, and I've been in groups where I've ran like hell with 3 mobs on me throwing out group heals to prevent a wipe.
However I don't tell groups that I'm discipline spec'd till after we complete the instance. What are some thoughts on holy versus discipline when it comes to healing?