Player can glitch thru a wall using a boat.
tested in 1.6 didn't work there.
only works in 1.7.2 in Creative and Survival mode.
extremely bad for multiplayer servers.
how to duplicate:
place a boat next to a wall (were the arrow points in the picture)
make sec wall so you don't tp there.
the West side you can keep open.
exit the boat using Shift will TP/spawn the player were the red circle is.
top of the picture is East, to the left is North.