Not too surprising when you think about it; it correlates well with high incidence of seasonal affective disorder and general lack of sunlight, as caffeine is a natural antidepressant. Same reason it's so popular in Seattle.
As an Italian coffee addict that moved to the States.. I can only warn you that measuring "productivity" in Italy can be a 'daunting' task. That being said, I'd be one more reader interested in the topic.
