I don't enjoy coffee, but I do make use of caffeine to stabilize my productivity. I buy it in pure tablet form, which is far cheaper than the equivalent amounts in soda or energy drinks, which I used before tablets and have now mostly stopped using due to dental issues.

I'm all too aware of caffeine tolerance, and I only recommend it in infrequent usages. Maybe you pulled an all-nighter two nights in a row and need help staying awake the next day for school, work, or what have you. Long drives are another case, but I don't ever have daily doses (anymore).

As for my productivity estimates when using caffeine, it's primarily a productivity stabilizer. When I use it in sleep-deprived states or for things that require long mental endurance, it puts me in a temporary (for as long as I keep taking it) pseudo-state that is as if I was in my normal one, decently-rested and alert. If I use it in my normal state, I get no productivity boosts. I suspect this is the result of a tolerance developed a few years ago.