My chests contained everything that i had amassed in the game, all my diamonds, emeralds, redstone, lapiz, coal, iron, gold, etc. I lost 3 level 3 enchanted diamond pickaxes, level 30 enchanted diamond shovel, level 30 enchanted diamond axe, level 30 enchanted diamond sword, level 30 enchanted diamond chest.
I have also seen that Legend Joe has been greifed, as well as Chess has been greifed and has all of his stuff stolen as well.