I'll chime in with what Buzzman has posted and say that bike commuting in Boston prevails purely by dint of the gorgeous scenery and the compact size of the city, and certainly not because of the poor infrastructure, aggressive drivers or clueless pedestrians. If anything, Boston commuters deserve some credit because they ride on despite all of those factors.

In the four or so times I've ridden my bike through New York, it's been surprisingly fun, because even though the traffic seems to flow faster than it does in Boston, the drivers all seem to be on the same page. They're all rude, but they're rude in the same, predictable way, so once you get that, it's easy to negotiate with them. By comparison, dealing with Boston traffic is like negotiating with a kid suffering Tourettes.

Though, really, my favorite city to ride through recently has been Paris. Combination of generous, distinct bike lanes and a prevalent bike sharing program puts that city in the win for me.