I tried my first-ever caffenol developer last night and was quite pleased with how it turned out. I'm definitely planning to do more prints with the stuff.
This contact print is on Ilford multigrade warm tone fibre paper, which I found gave nicer results with the caffenol than the non-warm tone paper.
Nick in Caffenol by Anthony DeLorenzo, on Flickr
My recipe was roughly 900 ml water, 6 tsp Arm and Hammer washing soda, about 30 500g Vitamin C pills, and 10 heaping tsp of no-name brand instant coffee. I was finding 3-4 minutes at 20-25 degrees was working well.
By comparison here is the same print on non-warm tone paper and developed with Ilford paper developer.
Nick by Anthony DeLorenzo, on Flickr