Rant: Magic Dust is dead

Magic Dust, that greatest of secret weapons, was destroyed by patch 3.2

It still has the same tooltip, but does nothing except say "fizzled."

See wowhead.com for more details.

RETRACTION: Magic Dust isn't quite dead, it just always fizzles if the target is higher than your own level (at least for PvE). It appears to fizzle at higher levels, too.