Sancocho: I mapped an entire 5 day ride into my Edge 305 earlier this fall. It worked flawlessly - I used MapMyRide to map the routes, then exported the .CRS files to my PC and imported the course files onto the Edge using the Training Center application that comes with the unit. On the ride I used the course screen and there were quite a few times when the cue sheet would not indicate a turn, but the GPS would. A few times I was able to confirm we were heading in the right direction in some rather rural areas of Pennsylvania. I couldn't, however, always say we were on the right road - just that we were on course, so it should be correct.
This, of course, relies upon the accuracy of the person (myself) creating the course in mapmyride.com.
Finally, when done I used SportTracks v2 to view my results.
It sounds complicated but it is exceptionally easy. I also uploaded to Motionbased so I could share the course and some statistics with folks following our tour from home, but I prefer SportTracks for my home based viewing pleasure.