I was playing around in the nether a while ago and i strapped on my Quatum boots. Now when i tried to power jump it launched my over 100 blocks forwards and about 40 blocks up.
i havent tried the Legs yet but im fairly sure they will make you Run 8x faster than in the real world.
it also does not stop 100% of damage more like 25%.
keep in mind this was tested on an SMP server with Buildcraft 2.2.1 installed
Edit: after some futher testing it found that it only occurs after going through the nether portal
not just going Into the nether but also while on the real world (recconecting fixes this)