Google Maps has added a new feature. http://bicycling.com/blogs/thisjustin/2010/03/10/bike-directions-added-t...
It's going to take some development work yet. When I tried it - using home and office as start and end points - it told me it couldn't calculate the distance, and the "bicycling" option from the drop-down menu disappeared.
In spite of that, it's a great initiative, and once they get it working right, it could be useful.