Do the top racers adjust the jib halyard tension during a race. I was talking to someone after last weekend's regatta and she claimed that she did and that it was faster.
That's the whole point of the "Z" routing of the jib halyard with the cam cleat on the side of the mast. Some racers will take up on the halyard downwind to pull out some of the mast rake (less mast rake downwind is somewhat desirable, especially in light air.)
How about the downhaul. Is it common to adjust the downhaul during races. I was surprized by this article which says not to worry about the dowhaul during races:http://www.hobieclass.com/site/hobie/ih ... ing_16.pdf
I'm pretty sure that article was written before the 6:1 downhaul with the cam cleat was class legal. Now that it is, it's much easier to adjust the downhaul. In lighter air, it certainly makes a difference, since the downhaul-induced mast bend will make the mast want to counterrotate off the wind.
Gavin Colby does make a good point though - all the tweaking makes no difference if you get a bad start and / or go the wrong way.