When Alice was updated to 1.2.5, I started having trouble with my jetpack. I got on, tried jetpacking over a low wall, and promptly hit the ground and lost half my health. Even if I use the jet pack to completely stop my fall, I get damaged just as much when I touch the ground. This is a little annoying as it makes the jetpack useful only as a convenient way for me to kill myself. I thought I should report it. Also the jetpack seems to have a delay sometimes, but that's probably just my crappy connection.
That is how jetpacks really are. Sk made it so that you would not take damage. That plugin was probably not loaded at the time. It should work now.
The problem was that if I jet packed up 50 blocks and landed on a ledge, I would take the damage from a 50 block fall.