I have collected proposal for 2 years and have got about 10-20g so far! I give away what I collect to people that ask for it, as I have never had enough to sell anyway. I have seen people selling piles of the stuff on ebay and wondered how they ever got so much. So I have learn alot from this thread.
The only place my bees seem to put it is on top of the frames where they meet the edge, or occasionally a little along the seal between 2 boxes.
I paint the inside of my boxes with polyester resin. The inside of my boxes generally stay clean. I wonder if the bees are happy with the polyester finish so dont feel the need to add more propolis, or if they hate it so much they wont touch it. Maybe my bees just dont make much, or perhaps there is not much for them to collect in my location.
Next time I make up some boxes I will try leaving one uncoated on the inside and see if it makes a difference.