On Normal I do the same as Disc. Last night i basically disregarded and kept groups at above 75% by combination of PWS/POH and Hymn. Add to that the wonders POM will do in the same situation.
Never been on heroic so cannot comment about it but POH seems a good idea as well as long as you are not the main tank healer.

Well PW:Barrier should still come somewhen. Though it's quite the question if only for 4.0 and cataclysm or before. I'm pretty certain it would be extremly desirable for those who are currently working at Anub'arak HM phase 3 right now.

Some of the posts about Anub seem to be about hardmode and others are about normal mode. In normal it is quite easy to just keep raid health high and to have everyone in a position where a Penetrating Cold tick is not going to kill them. Penetrating Cold does 3500 on normal (so max 3055 with a frost resist aura or totem and renewed hope/BoSanc) and the swarm leeches 10% (which should also get a 10% resist if you have enough shaman, but last I checked is unaffected by BoSanc/RH for some reason). That means if someone has 4055 health when they get Penetrating Cold, they will live through the next tick even without additional heals. Since everyone in the raid is losing 9% of their health every second, that means you need 365 healing per second to each person in the raid plus whatever tank healing you need and then reactive healing after people take the first tick. In a 10-man that means about 2.9k raid healing, in 25-man about 8k raid healing. Both are trivial numbers. This also means you are healing anub by the same amount, but that is a very small fraction of your dps.

On heroic the Cold ticks do 6000 (5238 through reduction effects) and the swarm leeches 20% on 10 or 30% on 25 (apologies if this is wrong, I used the datamined value from since I don't play 25s). That means that on the 10-person raid you need to have 9500 to live through the first tick, and in 25-man they need 13465 health. For 10-man that means you would need raid healing on the order of 1710 per person per second, or about 13,680 raid healing. Remember, that's before you heal the tanks or put extra healing on the penetrating cold targets. It also means you are healing Anub for the damage of more than 2 of your dpsers. This is mathematically possible, and the number is actually less than this as you are likely rolling Wild Growths or some other HoTs, but this strategy is completely outrageous. On 25-man the amount of healing needed to keep the entire raid at that value is unattainable, and would negate more than half your raid's dps if you could do it.

Power Word: Shield is the best tool to react to Penetrating Cold. It places a large instant heal on someone that doesn't increase the swarm damage they are taking in the next couple of seconds. A shield makes sure people live through that first tick, which is why I don't PW:S the raid during that stage of the fight. This is especially effective on 10-man where there are only two penetrating cold targets, because one priest can be in charge of making the penetrating cold targets live (there is no need to coordinate) which is good for reaction time. For these reasons, I ended up specing Holy with Soul Warding (Talent Calculator - World of Warcraft) so that I could shield the cold targets and cast more powerful direct heals (aided to a great extent by an always active test of faith) without using shield the rest of the time. Body and Soul was an added benefit to help people out getting away from packs of scarabs.

It's true that discipline has absolutely rotten single target healing output compared to the other classes (people mention shamans and paladins, but druids are also far superior in terms of direct heals), but discipline still proves extremely effective on almost every fight, because it has the best instant heal (it's a shield, but it does the same thing for raid damage) and is the only spec with real shielding capability. If tanks are taking their entire health pool or near that in single hits or short bursts bursts, or raid members are taking sudden massive damage that threatens to kill them in a couple of seconds then discipline priests are amazing. If not then they everyone going to get healed to full pretty quickly by any combination of healers (I don't mean to diminish the importance of other healers here, but unless you are bringing multiple discipline priests to the same raid then you are going to have someone else there, and any of them can do the get-the-tanks-health-up job very well). Basically, it is only in very odd situations (leeching swarm is one) that having the large disadvantage in raw possible hps is really a problem, and if it weren't for the fact that the power word: shield was needed for another purpose, shield-PoH spamming (or just PoH spamming) would rival any other classes raid healing capability. The problem with having lower hps numbers probably won't materialize until Blizz decides to go through with their supposed plans to increase health pools and slow down healing, which won't be until 4.0 if it ever happens at all, and then everything will be substantially rebalanced.

Do you think a Paladin or Shaman could perform the role of the Disc in that same fight? I'll agree you do not have nearly the raw HPS of any of the other healers when it comes to single target but, a Shaman struggles to do what a Disc Priest can do on that fight and a Paladin simply cannot.