I didn't raid 10-hard myself, but I remember hearing that Lich King 10 Heroic basically had to be healed by a holy pally and disc priest. (Shields helped with the plague, if a PW:Shield was absorbed completely it gave the priest back almost all the mana used to cast it. Beacon of Light was just really powerful in 10-man content overall IIRC because it was so useful to heal the tanks and spotheal.)
Edit: Yogg+0 greatly favored affliction warlocks because having to turn away from the boss in P3 just hurt everyone else too much and the DPS requirement was too tight.
Also, is there an ideal comp that could easily go through the entire expac? (Edit: the answer was to stack ranged)
How about Sarth+3?