Acclimation (t9) = When you are hit by magic damage you have a 10/20/30% chance to get an 18 sec boost to your resistance of that magic type. Stacks up to 3 times. (This is a very useful buff if the tanking environment will involve some consistant sort of spell damage. It may be a bit more situational though, so it may not be a full-time staple talent.)
Acclimation buffs Rune Strike (in addition to its normal effects).
If I go frost I'm taking Acclimation either way, but by buffing Rune Strike it makes it an automatic skill to take imo.