I actually went a little past the 1/2" radius roundover recommended in the manual, to a 5/8" radius, based on a discussion with the Kaholo designer, Larry Froley, and I'm very happy with it.  This is mostly about ergonomics.  When you are dragging yourself back onto the board after the inevitable fall, a soft upper edge is much preferable to anything sharp.  He used a 45 degree chamfer cutter in a router to eliminate a lot of the wood beforehand, and then used a round-over bit to finish it off.  You could also do this by using a combination of block plane and sander, or one of those Japanese saw rasps.  Draw a couple of pencil lines on the deck and sides to delineate how much to take off, and work to the lines.  The lines formed by exposing the different layers of ply are also a good visual reference.  Keep in mind that you have to have at least a 1/4" radius on that top edge to allow your fiberglass cloth to flow over it, so a sharp edge is not what you're looking for anyway.    

   Thanks that was super helpful!