The BBC does an excellent job of chronicling the various beliefs about safe coffee consumption. Over the years, scientists have disagreed about whether coffee provides any real health benefits and how much is too much. The only real area of consensus involves pregnant women. Four cups of coffee or around 200 mg of caffeine is considered safe.
For everyone else, the advice is no more than four or five cups of coffee a day. As with most aspects of our diet, the advice is moderation and variation.
Oh, and coffee is addictive.