"The English coffee house was crucial to the development and spread of ... The Englightenment, ... in part because of what people were drinking there." So begins author Steven Johnson's excellent TED Talk about ideas, and in part about how the rise of coffee changed the world. Another quote: "The water wasn't safe to drink. Effectively, until the rise of the coffee house, you had a population that was drunk all day." This is backed up by the real story of Johnny Appleseed, who was bringing a convenient source of alcohol (via crab apples) to America, not tasty fruit.
In an age when water was dangerous, most people added alcohol to make it safe; the coffee house (and in other cultures, the use of tea) changed that. Effectively, the western world suddenly switched its liquid intake, during the day, from a depressant to a stimulant. But there's more to it than that -- watch this awesome twenty-minute talk for a great story about coffee, coffe houses, ideas, and cultural interchange.
For more by Johnson, check out his books. I particularly enjoyed The Ghost Map and Everything Bad is Good for You (which is much more nuanced than many people would assume based on its title and associated PR).