I just re-activated Wow last night, and am still DLing the patch, but from what I was able to do yesterday on one shaman, while the patch was DLing, I'm uber-excited.

Elemental mastery, in addition to making instant casts and causing 15% haste for 15 sec, also ups damage by 15%.

The largest damage spell atm is not a nuke, ITS AN INSTANT CAST!!!!! Lightning shield stacks to 9, as you cast lightning spells (and the 5 hits from chain lightning can ALL charge the shield (60% chance)), and when you drop the instant cast earth shock for ~3k, you also drop the 6 extra lightning shield charges for ~10k, and crits for 20k !!!

Add in that you can do the classic, Hard cast nuke-> Elemental mastery -> instant nuke + rocket gloves -> shock +now 10k in lightning charges, I calculated that on a ~50% resil target, with 4 shaman, you can't do less than 54k damage, even if nothing crits, but since I have 45% crit chance and a 16% elemental overload chance, on average I would expect this to do more like 80K