I've been experimenting with coffee for a few years now, but I've never tried to quantify my results quite like the author did.

I've been everywhere from 1 cup a day to gross overconsumption. In the end, coffee doesn't seem to significantly impact my concentration. If I get 8 hours of sleep, don't drink any alcohol the day before, and stay hydrated, I can be productive no matter how much coffee I drink. Even more, I found that Morning Coffee makes me dehydrated and irritable, so I usually drink a cup or two after lunch to keep myself going. On occasion I've quit for 2 week intervals just to start from scratch, but quite frankly I'm addicted and never mind starting up again :)