With 9 others from my guild, I went and killed 5 bosses that were open for beta testing over the past two days. I did them all as Resto. I will try to get longer comments out at some point, but, here's a video of one of the more fun fights:
YouTube - Cataclysm Raid Test: Bastion of Twilight, Twin Dragons
--Still healing almost entirely with HoT's and instants.
--But mana is a factor. You can see me pacing myself through the fight.