I use caffeine actually primarily to control my ADD. The effect is harder to put my finger on, longer lasting, and more necessary for my work. If I am without caffeine for a couple fo days, my productivity drops modestly but that's ok. If I continue for a few weeks however at some point I may have trouble doing anything. I might spend all my time on HN at that point.

I do agree about energy drinks though. Tea works for me. I drink coffee in a pinch. Mix those with sugar and I can say goodbye to doing anything worthwhile though....