Earlier this month, I rode the End-to-End* using OSM on my Garmin as my primary navigation resource.
In a nutshell: it was great. 1104 miles covered in three weeks. All the way through, either using routing or moving-map display, it was reliable and accurate and just right. There was one dumb-routing moment (that farm track was not rideable!) and only a couple of ways absent from the map.
I had a couple of moments of drama that gave me warm fuzzy feelings toward the OSM community: one incredibly mundane - I was *desperate* for a loo and the tourist signs had me muddled; and one utterly critical - my old rear wheel collapsed and I needed a bike shop, urgently!
At this point, Bike Hub came to the rescue. Bike Hub is an app that uses OSM data so I was able to hit the "Bike Shops Near Me" button and -- joy! Dryburgh Cycles, seven miles away. A short taxi ride and I was repaired and rolling again.
I have, as the saying goes, eaten my own dogfood, and it was delicious and nutritious.
* Writeup to follow, honest.