I quit caffeine for a year but it didn't work out for me. I felt mentally sluggish all the time; there would be times I'd be staring at my screen with my mind resisting the act of processing any information. I also noticed I became very sensitive with how much sleep I got, and if it was anything less than 8 hours the day would be miserable. I could be a special case here with altered brain development since even as a small child I was drinking liters of black sun tea. So since my withdrawal experiment I've highly regulated my caffeine intake with pills with a maximum of 200mg a day before noon, although I will sometimes cut back to 50-100mg a day during periods when my life isn't running full steam. This has worked out well for me.