I know this one is from the history books, but thought I'd add for anyone reading in the future:
I put a very, very simple downhaul on our jib by using a length of 25' 1/8" parachute cord with a bowline at one end... Clipped the bowline in with the clip where the head of the sail connects to the halyard, then just ran it inside each hank as we bent the sail on, then right through the clip where the sail connects to the forestay--no block. I tied the loose end off to the center of the halyard cleat on the deck--the parachute cord is so fine it doesnt affect the halyard cleating, and that way it cant get away.
Our first sail was "eventful" to put it lightly, and being able to pull the jib down from the cockpit was really helpful. That system isn't as elegant as some, but it worked decently, and with a little trimming on the jib sheets the sail was secure to the deck without blowing into the water. We successfully launched and doused it several times that way. At the end of the day, the line stays clipped inside the hanks when the sail is put away, so there's zero additional rigging. It's about the only thing that went well this weekend!
Hardly an argument not to do it in my opinion.
Luke