This is something I've been debating fairly heavily from a personal standpoint, and also as raid leader of our small 10 man guild recently. How many Healers are you guys running with?
More specifically, which fights do you find that you NEED 3 healers, and which fights do you find that the 6th DPS really winds up decreasing the fight length/burn times (Putricide Oozes, as a good example) enough that 2 healers is AOK. Another way to pose the question; which encounters can 2 solid healers make their way through with a little extra help in the form of people doing what they're supposed to and avoiding avoidable damage?
I know raid makeup and skill can vary this answer a fair bit, so let's assume for the sake of keeping things on the same page that we're talking about a group of players that are skilled and geared enough to make steady progress through ICC10 and into H-ICC10 - even though the start might have been a little late =)
From a healing standpoint, we have a Holy Priest, Resto Druid, and Ele/Resto shaman that's making up the 3rd healer/6th DPS (and hucking out a few off-heals during heavy raid damage portions of a fight).
I can provide a WoL link, but I'm just looking for general practices from other groups, not tips specifically tailored to our group =)