Why do "Nitro Boosts" kill you now?

"Rocket Fuel Leak" was specifically meant as an alternative failure for dungeons, raids, and battlegrounds so we weren't launching people up into unknown invisible (or otherwise) roofs and getting them stuck or allowing content exploitation. In 4.1 it was fixed so that this failure was actually properly going off in these specific types of content.

Reevaluating the damage though, we're going to apply a hotfix to bring it down quite a bit (it won't be able to kill you outright anymore). Keep an eye on the hotfix blog as it'll be added once it goes through: http://us.battle.net/wow/en/blog/2690293#blog