@Ecnailla: Blizzard is in Anaheim, California (iirc)
@Irreverant: Void Reaver's knockback reduces the target's threat by 25%. If that reduction is sufficient to push someone else over the 110% (melee) or 130% (ranged) threshold required to pull aggro, off he goes. The knockback can miss or be parried/dodged.
Technically, to avoid pulling, melee DPS should stay below 82.5% of the current tank's threat, while ranged DPS should stay below 97.5% of the current tank's threat. All DPS must also remain below the threat of the offtank who is second to the MT. If you are higher than either of those values, you may pull if the MT takes a knockback.
Ideally, you should always try to be below the threat of all the offtanks. In practice, that's not always possible, which is why we use MDs to keep the offtanks' threat up.
All issues of buffs and class abilities aside, those are the rules to live (or die) by.
On a personal note, while I'm not intimately familiar with Hunter mechanics, I can say that I generate a very great deal of threat, and with no threat dump ability, I don't have the luxury of asking not to have Salvation. Going full-out DPS in the VR fight, while dodging Arcane Orbs, I managed to avoid pulling aggro while still coming in #1 on the charts. The primary reason I was able to do this was because I didn't die. If all DPS remain alive throughout the fight, we can easily beat VR inside his enrage timer. To me, that's a surer recipe for success than betting on one class to properly manage its threat.