The server is now restored with working Hey0 commands. PvP and monsters are disabled because Notch obviously did not fix many issues. Invisible mobs happen, skeleton's arrows are invisible to the player, and the client server communication for killing monsters (or your own death) is buggy. It's possible to get killed on the server side, alive on the client side, and walk around unable to die (since you're already dead on the server) or do anything. Hoping for some fixes soon.