Soul shards -- the special resource that has been iconic for warlocks since the beginnings of World of Warcraft. Once nonstackable in-game items that there were special bags for, soul shards now in Cataclysm are part of the unit frame as a secondary resource. Soul shards are particularly a great flavor match for affliction and will stay as affliction-only in Mists of Pandaria.
The only problem is that the Soulburn mechanic doesn't jibe well with affliction. Sometimes the stick is too long for us to care about the crunchy, delicious carrot at the end. Sometimes the carrot isn't big enough for the properly balanced stick. Whatever the problem is, our soul carrots don't match our soul sticks.