I don't think it's such a great idea. I don't think much of these things that plot your route for driving either. But at least selecting a driving route is a fairly straightforward exercise, drivers' requirements are pretty much standardized. Essentially, just pick the superhighway; if there is no superhighway, pick an arterial road. Even a dumb computer can do it. But for biking that would be essentially impossible to do a good job. Here is why:

1) There is no good definition of "bicycle-friendly" route. What is perfectly "friendly" for one cyclist is like riding through a minefield for another. Some people would go out of their way to stay on bike trails. Others would say bike lanes and quiet streets are acceptable as well. Yet others' only requirement is a wide outside lane, and some don't even need that. Some cyclists welcome a bit of off-road trail, while others on road bikes would not want to venture off pavement. The "best" cycling route to a destination is different for different cyclists.

2) Even if there was a good definition of "bike friendliness", the necessary data is just not there to plot it. Yes, some municipalities have bike maps that mark bike lanes, trails, "designated bike routes" etc. But there is so much missing from them! A bike can take a parking lot shortcut and end up shortening his route by a mile and cutting out a very nasty high-trafficked section of a busy road. A major arterial road might be extremely easy to cycle on due to a wide outside lane - and no cycling map shows it. Whereas a road with a bike lane may be worse than useless because the bike lane is right in the door zone.

The best way to figure out a route is to plot it yourself. Zoom in on Google maps to check road conditions and scout out possible shortcuts, get a local biking map - and you'll end up with something far better and more suitable for YOU than what an automated service can offer.