I've not actually boxed a 5 man team with a disc healer since wotlk, but Disc overall is quite broken atm. They've completely contradicted the entire "Prevent / Absorb Damage" that made Disc so unique and powerful. You get punished for throwing fast heals and shields around. They did buff Atonement's range, which makes it much more useful (5 yards VS 15 yards iirc) but in comparison with Holy, you're likely much better off with Holy @ 85. I raided, pvp'd as a Disc priest from Feb to Cata launch, and I'm currently running Holy because it's much more forgiving.