#0 - Sept. 28, 2007, 7:23 p.m.
It is currently -2/4/6% to instant cast spell cost, the change shown at blizzcon was that it also added 10/20/30% of your attack power to your +dmg/healing.
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Okay, right. Sorry guys. I've had quite a bit to keep track of as of late. That change is going into patch 2.3. But instead it will convert from spirit rather than attack power.
J/K =)
It's going in as described in this post.
Now on the EU listing of upcomming changes http://forums.wow-europe.com/thread.html?topicId=1017251722&sid=1&pageNo=1 there was an edit:
Update:
Mental Quickness now also adds 10/20/30 % of your Spirit to spell damage / healing
I find this pretty funny.