Absurd lag here too. Running on Vista Home, 4GB of RAM on machine and a decent graphics card. Vanilla loads up great for me. Tried turning all graphics down, turning the RAM up and it still takes a million years just to load up the world and then each step takes about 1-2 minutes and if I leave it running long enough it says it has run out of memory. Even the menu is incredibly slow to respond. Soooo excited about this release, hope a solution turns up soon.