For some time the C2C, Sustrans' most famous route, has been the most obvious omission from OpenCycleMap. Many of the long distance routes are now either complete or getting there - the Pennine Cycleway, Lon Las Cymru, the West Country Way, NCN 1, NCN 4 - but the C2C has remained only sporadically mapped.
When I tried to cycle the C2C the other year, I, er, fell off and mashed my face up. Other people are more competent than me and one chap has kindly allowed us to use his GPX tracklog.
So I've uploaded it and am working to map it with the help of NPE and existing, partly-tagged roads (ahem "only map places you've been" splutter). If you too are better at not falling off than I am, and have cycled the C2C, do join in.