It seems to me hard to really say whether caffeine is healthy or not. Rather the modern western lifestyle -- a lifestyle we've agreed to, or accepted, for the most part -- that has very little to do with biological rhythm needs to be evaluated for its health effects. As long as we're going to accept that everyone is going to work long mid-days in unison, sleep 8 hours per night, in unison, etc: then we're going to appreciate aids (fluorescent lights, caffeine, heaters, air conditioners, melatonin, food) that help us conform with everyone else.

Some may not feel they need caffeine as much as others: so be it. But the idea that any of us can really be deemed healthy or not, due to whether or not caffeine is part of the diet, seems to me to lose the forest through the trees