I started raiding like a month before Cata released. Yes, I'm a wrath baby. I don't find anything different as far as 'staying out of shit' goes, but I do find healing 100x harder now than it was in Wrath. Mana was not an issue, it was impossible for people to die really. I had 0 issues with going into Cata raiding/healing, but heroic 5 mans really helped with getting used to the chore healing is.