[karmamuscle]

Thou I haven't tried discipline yet, I would like to throw in my observations and experience, leveling in dungeons to level 84, so far, as Holy.

At first I had huge mana issues, oom after maybe 2 or 3 fights if it went well. Didn't it go so well I could go oom in a single fight.

What really solved my mana problems was when the other group players started playing more cautiously.
In Wrath of the Lich King you could pretty much plow through dungeons without ever needing an actual tank for 96% of all encounters.

This will not work in Cataclysm, as mentioned above, mobs hit alot harder now.
On the very first runs, a rogue would easily pass the tank in threat and get killed within seconds.

Once our dps only attacked the tank target and started to pay attention to their threat, I had zero issues with mana on trash and maybe lost half my pool on boss fights.
Also the AoE threat generation from tanks seems very very weak, strong single target threat thou. This is observation only, don't have a tank.

Another huge change for me, this is Holy specific but I'll throw it in anyway, is my own play style.

My main healing spell is now Heal. Throw on a renew and start the Heal chakra state.
The chakra state refreshes the duration on Renew and with State of Mind talents it adds 4 seconds to the Chakra duration when I cast Heal.
I can pretty much handle all trash fights like this.

On the AoE fights its basicly a matter of everyone being able to stand inside the Sanctuary while I use PoH and CoH.
If the fight doesn't allow everyone to be inside the Sanctuary, it gets kinda hairy for me...

Flash Heal is very expensive now and I only use it sparingly, since it can eat my mana pool in under a minute.
When I use it, its in combination with the Holy talent Serendipity.
2x Flash Heal and a Greater Heal, I mainly use this if something goes wrong and I need to top someone fast.