That is through the help of a tinkerer. The can make "junk" that does extraordinary things. See invis goggles, freefall and jumping boots. They are quite versatile.
its a glitch that could probably be mastered the more you mess with it. This isn't the first game that I would be involved in that has glitches that make you bounce unrealistically high though...hehe. Ask someone who does it, theres probably a little trick to it.
Yup, it let people jump to normally inaccessible places, or even through the "top of the world" and get away from MoB's or other PvP'ers. If you want to get away you have to run the old fashioned way.