WIndows 7,and 64-bit Java,with 2-Gig memory allocated.
When loading my 1.8 survival world to play it,i exited my house and a chunk was missing from the ground.It extended all the way to the void.No entities could enter the hole,unlike the previous bug back in 1.6 where you could jump in.My chickens couldn't enter,i couldn't enter,and,upon trying once,i lost some health and got pushed out,and water or lava couldn't enter.
Steps to Reproduce:
1.Load a 1.8 survival world with no cheats.
2.Look around where you spawned
3.Gasp at the giant surprise hole in the ground
(look at the attached files for proof)