Now I'm currently levelling my main, my Shaman, through the beta and am currently level 84. I decided to see what effect being a Mastery whore would have on my stats.
Mastery, put simply, for Elemental, is abso-fucking-lutely amazing. I'm hoping that it's not going to be nerfed for us come Live, it is that awesome.
For those of you who don't know, Mastery (as elemental)rating increases your chance for Elemental Mastery to proc - but the sweetner is that it now affects LvB. This leads to absolutely insane damage. I've almost one shotted similar geared players with a lucky Dual LvB CL strike - with crits that's a 30-35k boom burst.
Resto Mastery rating could do with some boosting as I couldn't really tell the difference, just remember Spirit is truly important now, without it you'll watch that Mana drain after a few Lesser Heals.
Enhance - I've not tried this yet, could do with someone's input here.
TLR - Mastery is awesome! Get it!