When my 4 shaman team is on their own(regular instances, no heroices, before level 60), I let them all cast lesser healing wave on 1 common target(which will be the focus or focustarget). However, when you're doing higher level instances(and especially heroics), it's probably better to let 1 or 2 characters cast a regular healing wave, because this is MUCH more mana efficient. It will also allow you to keep on doing DPS while casting the heal.

e.g. At level 52 I did a scholo run with a 68/69 tank and used 4 full Healing Waves to heal him each time. Lesser Healing Wave wasted too much mana.

[edit] http://www.dual-boxing.com/wiki/inde...ro_set#Healing
This is my regular healing macro as described in the first paragraph. As mentioned, it requires you to set a focus first.