I've used a battened shaped polytarp balanced lug on my Michalak Philsboat for many seasons now. I use a peak halyard to control the yard when lowering the sail and lazyjacks to hold the sail bundle. The light battens (there's just two of them) do double duty as reefing points and are attached to the mast with fixed parrels.
I've found the rig to be very well behaved on all points of sail and with that large wall of sail let out 90 degrees downwind the boat flys. The battens and fixed parrels ensure that the sail doesn't billow
when it's being lowered and also keep the strain on the polytarp fabric down so that it doesn't stretch.
A lot of polytarp sails are simply rags put up on a stick, but with a bit of thought your homebuilt sail can be effective. Over the years, I've taken a number of experienced sailors out. They come away scratching their heads at the utility, all round performance and power of a rig that they invariably pre-judge as being a toy.
Here's a YouTube video of her in action. http://www.youtube.com/watch?v=db2Jo9QAI3Y
> frank (didn't mean to rant)
> ps just to complete my thesis i would suggest that the Fully Battened Bermudan is the natural fulfillment of the (misguidedly popular IMO) Junk rig. - just don't use a bolt rope in a track - use slides or lacing so it dowses.