I do not know if anyone else has discovered this, but I have found something very useful. (especially for map makers) Normally you can climb vines that are on a block like a ladder. I noticed that if you are falling, and walk onto a HANGING vine, (not against a block), you slow down. I hit shift, like you can normally stop on ladders. You stop in midair, if you are touching the vine. Unfortunately, you can not move up/down. You can move side to side though. If there are more hanging vines nearby, you can go to those, and keep going. This would be great for custom maps, especially parkour. This was in version 1.2.3
I knew this, I think it was added in the first snapshot after 1.1. You're right about it being useful for parkour maps; in fact, I'm using it in my own!
r