David Johnson believes that genetics plays a significant role in whether coffee is good or bad for you:
If one thinks of coffee as a drug, then the notion that the benefits of heavy coffee consumption might outweigh the risks seems very counterintuitive. That is, due to the brain's propensity to maintain homeostasis, drug taking, either legal or illegal, usually involves some significant cost benefit analysis, a trade off between the good (the high, buzz, relief from psychic or physical pain) and the bad (side effects, withdrawal, expense, long-term effects on health, etc…) Yet, the evidence on long-term caffeine intake seems to put it in a distinctive class of its own.
More on caffeine's exceptionalism here. Johnson's explanation of how caffeine jacks you up is here. I could not live without it.
The Dish 