Thanks to the last Update, There is frequent lag pits, or in official terms, Chunk errors, in the Minecraft server.
What are Lag pits?
-This. This "Hole" from from another person's SP map.
http://t0.gstatic.com/images?q=tbn:ANd9GcS71SUyffcEsAQoQELg7UnR5JyaBuB05o8TvIjC1mo3SmpKVhhWeA&t=1How can we take advantage of it?
-It actually shows the Map's Contents, to a bigger degree, It shows the Map's Ores, Stones, Dungeons, and monsters.
-Its a Client-side error, relogging fixes it.
-By "Helping" another person as a guide where the Ores (usually Diamonds and Gold) People can get these ores easily.
From Wiki:
This is useful for finding caves and precious minerals. You should mark the surface in a memorable fashion above any interesting looking veins, caverns or dungeons before re-loading the map.
If you have a buddy on a multiplayer server with a chunk error, they are useful for guiding you from along the sides of a chunk error as they can see where you are digging. This means that your friends can point you to resources they cannot reach because of the chunk error.
Matter of fact, this is how i got Underground.