I have a multiplayer server, and when I updated to 14w33c from 14w32d, world holes started appearing, and once I fell into them, I could not get out, so I was forced to log out. When I logged back in, the whole world disappeared.

As you can see, the first screenshots are of the world holes, and the second is of the nothingness that follows a relog.

The nothingness has void like properties, as you cannot see yourself in third person.