Most of the important stuff have already been said, but I figured I would add some DPS vs healer gem disribution ideas.
Based on the calculations I've done for my paladin, fully raid buffed with full consumeables:
(comparison done both in terms of healing equivalent points and a % increase to current ability to heal)
+healing equivalent values:
for efficiency HPS burst (reliable)
sp+shaman sp only neither
Spinel 22 22 22 22
pyrestone 18.05 18.325 20.325 12.925
amethyst 18.58 19.88 24.54 11
lionseye 14.14 14.14 14.14 0
sapphire 15.16 17.76 27.08 0
% increases:
for efficiency HPS burst (reliable)
sp+shaman sp only neither
Spinel 0.814 0.814 0.814 0.468
pyrestone 0.668 0.678 0.752 0.275
amethyst 0.688 0.736 0.908 0.234
lionseye 0.533 0.533 0.533 0
sapphire 0.561 0.657 1.002 0
According to these calculations it all depends how likely your pallies are to get shadow priests where it matters. Anyway you can see the highest efficiency you could possibly get from a gem is 1% from a sapphire without a shadow priest which is the least likely scenario. The burst HPS increase of a spinel is less than 0.5%. For comparison a DPS caster would gain something at the area of 1% DPS from a spinel. That generally means spinels should go to DPS.
On top of that, increasing raid DPS reduces the fight duration and thus the amount of healing needed and is an actual additional boost to the healer's ability to heal (only on the efficiency portion, though).
Since I bet the relative increases of other healers aren't significantly bigger, added to the fact that more dps = shorter fight, just make your healers choose if they want living rubies or shadowsong amethyst (assuming all your dps already have 2 for their meta gems wherever applicible).