Twice now, I have deliberately gone cold turkey on caffeine for a month. Both time, the results were the same; while I didn't completely lose my programming ability by any means, I totally lost my best programming times, and in general felt slower and fuzzier even during the rest of the day. From what I can see, after a month off of it I should be adjusted to its absence.

Since then my situation has been changing some, and once it stabilizes I plan on trying again (learning I have celiac disease, changing some other elements of my diet). So this may not be generally applicable. But I will say that if you are nervous about your caffeine consumption, try dropping it for a month and seeing how it goes; it's not that hard.