Every 100-200 blocks or so, blocks won't load for up to 30 seconds. Even worse when playing couch co-op. When placing blocks, they lag, when opening menus, they lag. When opening up the skin selection screen, it lags. Before the 1.8.0 update, the game would load fine. World is only about 83mb big, so I really don't think the system should be struggling at this point. The 1.8.1 update fixed, at least, the saving issue, and I haven't worried about falling from the sky since then, but this lag makes the world pretty unplayable, and it's no different on new worlds or creative mode.