I give up coffee every year for at least 40 days. It takes at least two weeks to start being as productive again, but after that cooling off period my productivity begins to rise. I have more energy in the evenings and sleep less.

+1 for the give up coffee advice.

My 40 days is in observance of the Christian Lent period. I'm not Christian, but the 40 day stretch is as good of period as any to make a change in your life, and I like that I observe the same rituals of many of those around me.