My own Death Knight is not quite up to raid tanking yet; I've got a few more levels to go on that one. However, some players have noticed that DK threat, especially on single targets, seems a bit low - significantly lower than the other three tank classes, to the extent that the tanks were having trouble keeping threat against high DPS.
It turns out that there was a slightly complicated bug involving Frost Presence, the foundation of DK tanking. It went like this:
- Some aspects of Frost Presence don't go away when you die, and some do (this is the bug).
- Part of the threat boost, however, does go away when you die.
- When you res and come back without changing presences, the game doesn't reapply Frost Presence, because it sees that you already have some of the effects of it.
- However, you still don't have all of the threat boost.
So potentially, DKs who die and come back without switching to another presence (Blood or Unholy) and then back to Frost were missing out on 15% of the 45% threat that Frost Presence brings. This has been hotfixed now, so there is no further need to worry about it. If you saw your DK threat go up a lot yesterday, that's probably why.
Ghostcrawler adds that "it is likely" that Defensive Stance was also being affected by this bug, although I haven't seen any prot warriors complaining about their threat since 3.0 hit.