No kidding - Mastery is terrible for Resto. I would personally recommend any green quest trinket over the Tol Barad mastery trinkets - I mean, you can't even reforge the mastery off of the epic one because it's on the proc. And if any Resto Shaman has a "hankering for mastery," they oughta get a totem upside the head. As per the Resto thread at EJ:

Q. How good is Mastery for us?
A. Pretty sucky. While we don't yet have any way to determine just how bad it is, Mastery doesn't end up saving us mana, has about the same effect on single target healing as crit without providing Ancestral Awakening or Ancestral Healing procs, and in terms of Chain Heal throughput doesn't hold a candle to haste. Go ahead and reforge all your mastery to something else.

http://elitistjerks.com/f79/t110263-resto_cataclysm_raiding_discussion/

Indeed.
They should make mastery for resto shamans grant an increased crit chance based on the health percentage of your heal's target.
That could end up being broken, but at least it wouldn't suck.

I can't see how the resto shaman mastery would be "poo"... Additional healing based on how low the target is? That pretty much defines the "triage" healing style in Cataclysm. It's kinda lousy for Tank healing, sure, but that's never been a resto shaman's forte.

However, if you look at it, Mastery IS a resto shamans healing cooldown - You get the most when you need it the most. And that's a very shaman way of doing things: fluid & effortless, as long as you follow the ABC of shamanism: Always Be Casting.

Yeah, I cringe every time I see a massive lump of Mastery on our gear, so much wasted potential. I really do hope they re-evaluate it and tweak it to be more attractive.

Vogie, it may make sense thematically but that doesn't make it a desirable stat to a Resto Shaman. The numbers don't lie - if you stack mastery, you won't be as good a healer as a Resto Shaman who avoids mastery like the plague. Consider the comparison to crit: crit and mastery both increase the amount of healing done, but crit also gives you mana through Improved Water Shield, along with even more healing through Ancestral Awakening, and a valuable buff in Ancestral Healing. Mastery just doesn't cut it, no matter how you look at it.