I do a full month a year with no caffeine. Partly just to prove to myself I can. Headaches first few days and it wears off. When the month is over im back on 2-3 double espressos a day. I enjoy a good cup of coffee, so I decided not to care about the downsides.

I once read "why we sleep" which basically says coffee is crazy bad for your sleep even if you feel like you sleep fine, you're not sleeping deep enough with coffee after 3pm, I think it was.