So I healed my first heroic last night, didn't even wipe on the first boss (though it was damn close)
Darieth hit the nail on the head with regards to not keeping everyone at 100% the bigger health pools everyone now has means they can take some punishment regardless of class and they're not going to suddenly fold.
My biggest issue is the manouverability problem, in some fights there are things you gotta get out of and you cant cast heals while your running (at least as a priest). Against Lockmaw, the dmg he did to the tank needed constant healing, the 14k a tick poison dot I can't dispell was on various dps AND I had to run around meant we just couldn't get the boss down.
That said, its a million times more fun than healing in wrath. We're weighing up the pros and cons of each heal on a heal by heal basis.
The top things I feel I can add for priests are:
Binding Heal = very mana efficient way of healing u and another person, I get it critting for around 18k + 30% as a Divine Ageis shield
The talent where every greater heal knocks 5seconds off your cast time for inner focus is one of the BEST things we have. My inner focus is never off cooldown, either use it for a nice top up POH (again its healing on crit for about 10k, plus around a 3k DA shield) or a big ol' greater heal, giving a tank with grace a 30-35k heal and nearly a 10k shield as well. Thats a free 1/3 of his health almost. Just wish i could solve the problem with movement!