I've used ridewithgps quite a bit and the authors have improved things greatly. I generally download gpx or tcx files to my computer and simply transfer directly to my 705, but ridewithgps supports direct download to Garmins. I believe there would still be issues in going back after the fact and adding coursepoints to overlapping portions or a route, but you can overcome this by adding rest stops and such as you build the course.

Mapmyride is useful for accessing others' routes, but the ads are annoying as is the overall interface. I've not had good luck with bikeroutetoaster.