If you have a world that was generated before 1.7, and you go to explore more to find things like new biomes and plants IN that world that was updated to 1.7, the newly generated areas are VERY, VERY laggy and have massive lag spikes about every 5 seconds. It would be much appreciated to have Mojang think about the people with existing worlds, like Apple gives much consideration to people with existing data and allows you to bring things up through the versions. Majang need to make things like newly generated areas and worlds work for all, new and old alike, and make them work well. If you guys could find a way to improve stability, that would be down-right fantastic.