The proverbial light went off in my head when Miguel mentioned using reflective tape on his guy lines. A high visibilty solution isn’t good enough at night because of our eyes diminished ability to discriminate colors in low light situations. His reflective solution is far better.
So I ran down to the local auto parts store and picked up some conspicuity tape that costs about $2 for a piece 2″ x 18″. It weighs 8 grams (0.22g per sq/in) including the backer sheet on the adhesive. For less than a gram you can apply this to your complete set of stakes. 3M guarantees this tape for 7 years on the side of a cross country trailer that will be in the elements for 99.99% of the time.

The nail stake (top) has no problems.
On the 4mm stake (middle) the exposed end of the tape is trying to peel off. I’m going to try clear shrink tube over it tomorrow to prevent this. I’m unsure how this will affect reflectivity.
On the 3mm stake (bottom) the 3/8 x 3/8″ flag appears to have adhered to the stake well. Time will tell if it is durable enough.
I was a little disappointed with my first field tests. I found the light reflected back toward the light source in a very narrow cone. This means you cannot search for a stake with your flashlight at waist level because the cone of reflectivity is well away from you eye. If you raise your flashlight up nearer eye level similar to a headlamp the tape reflects quite brightly. If you think about it this makes perfect sense.
Jason – I used 1/4″ with a 2:1 shrink ratio. This is the standard stuff available at any electronics supply store. The stake is 4mm dia.
Mark – regarding recovery, after the tube is completely shrunk it is recovered. The supplier mentions this because tubes have shrunk in shipment in hotter weather. This is a bigger concern with the higher shrink ratios (3:1 and 4:1). They encourage people to purchase in cooler months if delivery is required.