Jump...hmm.
From what I see, it is very little server-side control.
The moment you click a spot to jump, the server essentially acts as if you are there already. You can notice this by how monsters will begin to move to you b4 you even arrive. So, the moment you click, the server agrees that you have arrived at point xxx,xxx; Then your client initiates the jump animation. Speed"hack" makes this animation faster, making you able to tell the server new coordinates sooner. As long as the coords are withing a set window, the server will agree, without really checking the time between the sent coords. This is why ppl see you as teleporting, the server hasnt told them that you are using "cyclone". If you DC, you will see a msg at the top left saying "invalid jump", meaning you went out of the designated window or jumping locations, or you overflowed the jump packets sent (OK, so there is a slight server sided time checking thingy...maybe).
Thats just my opinion. Most likely wrong or mostly wrong lol.
You win some you lose some.
--Katsu