Sometimes I feel like I can't get away from Illuminated Healing. Our holy paladin mastery has been receiving nonstop tweaks since its introduction, and it's always flirting with viability. Stats like haste and critical strike rating are predictable. I can draw up some formulas to show you how many extra ticks of Holy Radiance you'll receive at a given haste level. Mastery is much more nebulous than that, as its effectiveness depends entirely on the encounter and your healing assignment.
Everyone has some amount of mastery rating on their gear, and there's even some passively built into our characters. While having a bit of mastery to make our heals bubbly helps our throughput, it's certainly not overpowered. There are a few holy paladins who, in an attempt to see how far Illuminated Healing can go, have enchanted, reforged, and gemmed into mastery completely. With IH bubbles absorbing 35% of the value of the original heal, stacking mastery can obviously make something interesting happen. How potent can Illuminated Healing really become?