I,too,have spent many comfortable nights under a poncho/tarp rig and they can work quite well if properly rigged. Size matters.

I often carry a light weight tarp fashioned from painter's tarp material which is light but not all that durable. This works well in situations where I find the poncho cumbersome (thick brush, technical climbing terrain, etc) and I don some sort of rain suit.

I like Montanero's list of essentials. Throw in a Bic, a small flashlight/headlamp, and a bit of FAK - you are good to go.

Bottom line - there are few pieces of gear more versatile than a poncho...