Actually mastery can be and is calculated. Especially for holy pallies and druids. Druids always have HOTs rolling out since that is the main way Blizz has decided to deal damage and make healing "interesting" for raid healers - they wouldn't be raid healers if only 2-4 people were taking some sort of damage. Aura damage like from Sindragosa - and from the new Cata raids which are being tested bosses have specific abilities which will destroy raids - and we'll have to heal them up.

Back to the point though - mastery will be calculated via chance of proc, size of proc, and how much healing those absorbs do vs. a pally who decided to not reforge or instead took a piece of gear with less mastery for more crit or haste. It will just take time, however, I say by end of December we'll have an excellent idea of what numbers to aim for.

If you did any hardmode ICC's and healed more than just tanks (i.e. beacon and heal the raid) and had your holy light down to GCD it's amazing that you never previously used LoH as a mana battery. That's the only thing I ever used it for besides Festergut when it was called for as a tank cooldown. I found the excitement in raiding in healing as many targets as possible before the raid healers could even react. It was fun and it was a challenge to my fellow healers. As long as everyone stayed alive - it was pretty awesome.