Ponchos are not nearly as warm as rain parkas in cold & rainy weather. Also ponchos, being of non-breathable fabric, get very wet around the shoulders and upper chest.

In warmer rainy weather I wear my Cabela's PacLite poncho over my pack W/ the hood on my head and arms wrapped around my lower shoulder straps. This gives enough protection in a light rain and keeps me from sweating inside the poncho.

Eric
_________________________
"There are no comfortable backpacks. Some are just less uncomfortable than others."