In both my groups (5xdruid and a Paly/Mage/Shaman/Priest/Druid group) I use the number keys to handle most healing. I run on the principle that my tank in each group will be taking 90%+ of all the damage, and my healer should be taking the absolute least. All of the macros on my healer toon are set to either /target Party1 (the leader) or /assist Party1, in case my leader dies and I need to switch leads, I can still heal.

Number key 0 on the numberpad I use for emergency heals to the healer himself, just incase. This is my rejuvenation/swiftmend to my druid healer key. Number key 1 does an HOT on the tank, or a lifebloom then a rejuv/renew. Number key 2 does a bigger heal, ie: Regrowth or Flash Heal to the tank, number key 3 does a big heal (Healing Touch/Nourish/Greater Heal) to the tank. So these ones use /target Party1 for their target.

Number keys 4, 5 and 6 are the same spells, just using a /assist Party1, meaning my lead toon needs to target the character that needs healing first. I'm thinking about changing this to a focus target, and then either predefining a focus target on my tank by guessing who might take extra damage in the upcoming fight, or use mouseover macros to assist focus targets on the fly for healing, without having to drop my current tank target which my dps relies upon.

Then for any aoe damage taken by the group, I have just a regular bar icon on a regular number key assigned on the healer that casts whatever my group heal is, and if needbe targets someone. For my druid group, I target /Player on my healer (targeting self) and cast Wild Growth. This assumes that my tank is getting topped off my the existing HOT's on him, and the rest of my group are casters back with the healer, so that'll hit all of the group besides the tank.

I also have setup F1-F5 to cast a Regrowth/Flash Heal on that party member, so unbound those keys from all the other toons including the tank, and bound them for the healer to do a /target Party1-4 or Player and cast Regrowth.

Works well so far, though if things go south and my healer dies I'm pretty much SOL, so I'd like to put the same macros on the other healer capable toons with conditions in place that if the healer is alive, don't do anything. Just as Redbeard described.
Cheers