If you're here already, then this is important information. When 1.2 is released, all survival maps will be removed. Therefore, do not build anything you do not want to loose! Feel free to gather whatever resources you desire, there will be a time when the current 1.1 map and the new 1.2 map will coexist and you can move your items via common portals which will be set up.
This does not affect the superflat creative. There are no terrain updates which affect that world.