It's inspired me to start mapping some of the NCN routes I've cycled, with GPS, over the last couple of years. This has also been made possible by Potlatch's new magic 'U' key, which converts unwayed segments that someone has "helpfully" drawn very approximately along the line of my GPS tracks, into a nice editable way.
So I've recently drawn the Pembrokeshire/Carmarthenshire circuit on routes 4 and 47, and a couple of others that don't show up on the map yet. I've got tracks for much more of routes 4 and 5 to work on, and went out last night to get the missing bit in route 54 from Burton to Alrewas. The truly splendid route 8 - Lon Las Cymru - I cycled without GPS (shame) and will have to be an NPE job. Which means I'll have to remember how to use JOSM. Eek.