As most of you know, our favorite exploring bug, mounting through walls, has been severely nerfed with the release of 4.0.1 . Mounting in front of/under a wall now dismounts you consistently every time. You can, however, still use mounts to get through walls(though it takes significantly more work now). Though you are dismounted right away, you can still run and jump forward just as you mount, giving you some slight momentum through the wall before the game can dismount you. If you are persistent, most of the old mount-through-walls locations do still work(though it may require a bit more of an overhanging wall to pull it off now). This Youtube video demonstrates a few of my favorite old locations(yeah I know you can see names, I don't care. If someone could tell me how to edit that out with free software, I would be grateful).
edit: cropped out my name, let me know if you still see it anywhere.