The bicycle routes option on Google Maps is too new for me to have used it very much, but it is a tool I will use in the future. I'm sure there will be many times that there is a better option than what it suggests, but I have already seen some suggested routes that look like they may be better than what I have been doing. Assuming it works like regular Google Maps, you can make changes by dragging points to different roads and it will reroute to compensate.