I have a Garmin 750 and download the routes from the Harley Trip Planner.
I have noticed that it recalcuates my routes at times and takes me around some of the places I wanted to see. it's hard to review it on the GPS at times.
I have to put lots of waypoints in the trip to get it just the way I wanted it.
Once it had me get off the highway, takes me 2 miles down a road in Tulsa only to do a U turn and back to the road I was on.. But if I had to pick on out there, it would be the Harley Trip Planner.

 

Try out this application made to be used with the Tom Tom and Google Earth. It will work with other GPSs as well.

http://www.janboersma.nl/gett/

It's called TYRE or Trace Your Route Everywhere.