A recent trip where I forgot my umbrella had me using my polycro ground sheet as a rain shawl. I draped it around my neck and criss-crossed it in front, trying to leave as much covering my shoulders as I could. My backpack waist belt held it in place. My sternum strap went beneath the plastic. My camera hangs from the sternum strap and the plastic kept it dry.
I can't say it was the most effective, but it did help a great deal. My torso stayed dry. My camera stayed dry. It was warmer wearing it than without. It was raining as a fine spray and not heavy rain.
Anyway, it was a back-up plan I always kept in the back of my mind and finally had an opportunity to try it and it worked. YMMV.
