I tried the Google Maps Bicycling option on some city, suburban and rural routes. There are still quirks in both the maps and the algorithm. I imagine some of the issues will be fixed in future releases.

In rural areas it frequently uses gravel roads rather than using low traffic state routes. This is especially true of long distance routes, such as Chicago to Omaha. Over long distances, the routes suggested with the Bicycling option are often the same as one gets when using the Walking option.

Then, oddly, it uses some very high traffic volume streets passing through some towns.

On the plus side, it frequently offers several routes to pick from, one of which is likely to be reasonable. And it is easy to recalculate a new route by dragging and dropping some points from the initially calculated route.

It was helpful in cutting 10 miles off of a 50 mile trip from Homewood, IL to the Indiana Dunes SP, but it took a lot of manual tweaking to get there.

Bike routing around Chicago looked pretty good. In both city and suburban areas, there were several odd cases where, when roads intersected, it avoided the intersection by zigzagging thru residential areas a few blocks from the intersection. It appeared to not like to route thru the stop light. In both the city and burbs routes sometimes zigzagged on and off of a perfectly good street, including some streets with bike lanes.

It doesn't know about a number of good county bike paths. And it is currently missing two of the longest bike paths in the state of IL ... the I&M Canal from Joliet to LaSalle (approx 60 mi) and the Hennepin Canal from Bureau Junction to Moline (also approx 60 mi) I presume these oversights will be corrected with time.

The most important ( to me ) features of google maps for bicycle route planning are available regardless of which routing option is selected, walking, driving (no highways), or bicycling.

First, a route can be displayed along with selected points of interest. For example, the location of campgrounds, or convenience stores, or restaurants, or motels, or whatever services are of interest, can be displayed on any route you select. You manually tweak the route to take advantage of them. That is extremely helpful in planing a long distance tour.

Second, the mapping options produce a cue sheet.

And third, street view is often available along the route, so you can get some idea as to whether or not you really want to bicycle on a particular road or over a particular bridge.

The Google Maps bicycling and driving (no highways) features strike me as useful tools for initial route planning used in conjunction with, but not instead of, state and city bike route maps. And I would still bring maps and/or GPS on a tour.