But, wait! Look! They now have bicycling directions in beta.
The other three tabs at the top left are for driving, walking, and public transit.
As far as I can tell, it only works in the US and Canada. I tried to plot routes in England, Japan, and Mexico. None of them worked. And when I tried to plot a route from Vancouver, Canada to Toronto, almost all of it went through the US. So, it's a little biased towards routes in America.