When your raids are populated via sign-ups as opposed to being hand selected by officers, you start to notice some pretty interesting trends. A few months ago, we had more druids than we could handle. Then all of a sudden they all disappeared, and we had no druid healers.
We haven't had a shortage of healers in general as of late, but our mix of healers has been less than ideal. One week, of our 6 healers, 4 were paladins. This has repeatedly been a source of some strain for me.
I like to come up with new words, so therefore I have now coined the term "Overpallyfication" - the overabundance of single target healers within your raid makeup, with Pallies being the best example.
It's not exactly new information that "all healers are not created equal". And perhaps I am a little OCD about healer makeup. But, 7 healers (4 of which are pallies) is better than 5 healers at this stage of the raiding game for us. I have actually had to turn healers down because of overpallyfication, but I don't want to continue to do this. At least with the 3.2 pally changes, it will be a lot easier to justify extra pallies, due to the changes in Beacon of Light.
Too Many -insert healer type here-
So what do you do when you have an overabundance of a single type of healer? Interestingly enough, there are some healer types that don't really present too many problems if you have too many. Holy priests are the perfect example of this - because they are the jack of all trades amongst healers, they can handle single target or raid healing without any trouble. If you had 7 holy priests, while it wouldn't be ideal, it would probably not be too much of a problem either.
This is not the case with Discipline priests. Bring 7 Discipline priests, and there is going to be a lot of frustration amongst them. Disc priests are all about teh bubblez, and you can only have one bubble on you at a time. Whereas with other healers, you can get two heals from two different healers at the same time without a problem, you can't have two bubbles from two different disc priests. In addition, disc priests' strength is in the special bonuses they get from healing someone who has a bubble on them. Matticus actually wrote a somewhat interesting article about multiple disc priests on wow.com the other day, but he focused more on whining priests than the actual potential problems of multiple disc priests. I don't think there's a problem with having two disc priests, but once you get more than that, it's going to be a struggle. If you do have multiple disc priests, you need to be very careful to give each priest their "territory" per se. If they don't have healing assignments, they are going to overlap - and bubbles do NOT overlap, so there is going to be a lot of time wasted between the two of them.
With Druids, you can handle a lot more healing druids in a raid than say, Discipline priests. However, like disc priests, Druids have a very interesting healing mechanic - the HoT. The thing about interesting healing mechanics is that they are a really great addition, though in a tight spot you can do without them, and an entire raid based on those "interesting mechanics" will likely not go well. I have no problem with having 2, 3, maybe even 4 druids. If half of my healing team is druids, I don't find that to be a problem - however, more than that and it will be difficult to deal with burst damage.
Of all the healing classes, I will be the first to admit that the one I understand least is the Shaman. This lack of knowledge on my part means that I tend to underestimate the shammy healer. This is partly because we only have one regular shammy healer in our alliance. There's no question that he is a fantastic healer, but I really don't have as much experience with shammies, though I'm working on that. That having been said, like priests, Shammies are good overall healers. They can handle the raid and they can take on single targets. The biggest problem I actually see with too many healing shammies is that the awesomeness of their totems can quickly go to waste due to lack of stacking. This is the only reason why, even if given the opportunity, I would shy away from having more than a handful of Shammies in my healing makeup.
And now we come down to the Pally. A really strong pally can seemingly heal forever, drop spam bombs like nobody's business, and overheal without too much concern anyway. However, with all the raid damage going over in Ulduar, it is tough to have too many pallies, because let's face it - they aren't strong raid healers. Even with Beacon of Light, and even with the incoming buffs to Beacon of Light, it will still be difficult to justify more than 2 or 3 pally healers in a 25 man raid. The good thing is that the various fights in Ulduar seem to require multiple tanking roles, unlike what we saw in Naxx. In Naxx, two tanks and you were pretty much set. In Ulduar, three tanks is cutting it close, in case one dies. Therefore, I give each of my pally healers one single healing target - one of our tanks. In the past I've left their BoL target up to them - with all the raid damage, it's not a bad idea to have themselves set as BoL - and this also helps if you have a shortage of raid healers. However, if you're going to have a handful of Pally healers, they need to be on the ball. They need to be literally spamming their heals, because a tank going 6 seconds without a heal very quickly becomes a dead tank. In addition, if you're going to give each of the tanks only one dedicated healer, those healers should be similarly capable of handling the incoming damage.
Focus on the strengths! /flex
So, in summary, what do you do when you have an overpallyfication problem, with too many single target healers? With pallies, I give each tank a dedicated pally healer, and it's really important to get across to these healers that they need to be only healing their target - don't try to raid heal, or the tanks will die. If I had fewer single target healers, I would double up the dedicated tank healing assignments. Even with dedicated heals, we still need druids and priests to HoT and bubble the tanks regularly. With too many disc priests, you again need to emphasize specific healing assignments. Give each tank a dedicated healer, and if you still have extra single target healers after that, with priests you can let them focus on bubbling specific raid groups, and using Prayer of Healing during phases that include XT's tantrum, or Ignis' flame jets. Disc priests and holy pallies can also handle certain "bomb emergency" aspects as well, such as Slag Pot, Searing Light, and Gravity Bomb. Between Holy Shock for pallies, and BubblyBubble for Disc Priests, even these single target healers have strong mechanics for healing "bomb emergency" mechanincs - as long as their reflexes are strong, and they are paying attention.