I’m a board game fan myself, but I know that millions of people spent their Christmas exploring the underwater realm of Vashj’ir, thanks to the online computer game, World of Warcraft, which launched a new version, Cataclysm, in December.

Loyal readers will know why economists find such games interesting: they are virtual worlds in which millions of people spend many hours interacting, creating experiences and goods that other players value, and even spending real money on virtual items. (Crazy? No more crazy than paying to watch a movie.)

Facebook applications such as FarmVille have many more users. But it is the great online role-playing games – and none is bigger than World of Warcraft, with 12 million users paying a monthly subscription – which hold an enduring fascination for the way that they blur the line between virtual life and real life.