Ok, after watching all Kartseven videos, i've a newbie question:
there is a way to jump faster than just press and release the  
L button?  

termoPilucco

on a serious note, i imagine its to do with starting to turn into a corner then tapping jump or tapping jump and turning at the same time into a slide

I don't think there is a difference ! If I jump more, it's just cos I'm a SMK driver, so I kept this driving's style !

I'm not sure if this is still relevant these days, but I used to jump a lot. It was really good for quick trajectory changes if I recall correctly (almost as good as a mushroom! =P).

But from what I remember, it screwed me over on the water levels (KB2 is a prime example). Apparently there was some sort of slide you did through the water, which I never really mastered.