Diablo,
I don't know what Rob did, but if I hooked a jellyfish I'd just do the same thing as when I hook a bull frog or something. Grab the shank of the hook with a pair of pliers and shake shake shake. It'll pop out. With a jellyfish you could probably just rip the hook out since they're so soft. One quick jerk of the rod should do it. The only dangerous part of a jellyfish are the tenticles. You can actually pet jellyfish on the top of they're blob without getting stung, so that's something to consider if you ever snag one. If it's red in color and looks kind of solid, DON'T TOUCH IT!!! Thems the bad ones. Most will just give you a little sting that'll go away in a couple days. They can't sting through wetsuits or waders, so your legs are safe.
-Brian