Historian Niall Ferguson ably summarizes the familiar data on how much less Europeans work than Americans and then offers a very provocative explanation:
I cannot resist suggesting another possible explanation - one that owes a debt to Weber's famous essay The Protestant Work Ethic and the Spirit of Capitalism, which he wrote almost exactly a century ago.
Weber believed he had identified a link between the rise of Protestantism and the development of what he called "the spirit of capitalism". I would like to propose a modern version of Weber's theory, namely "The Atheist Sloth Ethic and the Spirit of Collectivism".
The most remarkable thing about the transatlantic divergence in working patterns is that it has coincided almost exactly with a comparable divergence in religiosity.
It's the sort of theory tailormade for somebody with my particular set of biases, so I'm forcing myself to be very skeptical. In any event, do go read the whole thing. It's very well done.