http://img808.imageshack.us/img808/3650/float.png
Messing around with some floating blocks.

how do you do that?

Are you a wizard?

Deuce22:Dustmako is the last person i would ban

I wonder why, maybe because he is a fucking magical jejebaba kodaro shovel wizard.

Lag.

This is a lag exploit. If you're pillaring straight up and somone breaks a block at the bottom while you're still building, you can end up with floating blocks. If you place a block from your client after another client has broken blocks but before that change has made it to your client, the block will float and support other structures. Shield the block from griefers and you can make a floating palace (The easiest way to make a "safe" sky palace is to have a lagging friend help you make the floating block, and then build blocks on the underside of it so nobody can break the block easily from the ground. Build it up from there).

Be warned, though... since this is a bug, your floating strucutres are prone to failure from a variety of reason... it's possible that the whole thing will fall if even a single block is broken from the structure. Don't make any floating structures too elaborate.

If you place a block on a floater then chip it off again, it always falls down.