45%ish on Kel'Thuzad. Entire instance has gone absolutely perfect.
Ret Pally gets Detonate Mana. Starts to run out, gets hit by Frost Blast. Catches the two melee near him at the same time. Frost Blast ticks twice, Detonate Mana goes off. Two melee are dead in under 2 seconds.
Guess next week we just won't have people with mana bars in melee range.