I recently went 60 days without coffee and had only one cup of tea or chai a day. Basically my productivity went down. Then one day, out of desperation to get work done, drank a single cup of strong coffee and subsequently had mild insomnia that night, but, my productivity levels went up. I really enjoyed the coffee so I went out and bought some very light trader joe's beans and some decaf. I mix the two. I don't have sleep problems and enjoy my coffee in the morning. I try to not drink coffee on Sunday but I find I have a cup right now while getting some client work done.