I work for Mapbox. We have some teams dedicated to improving OSM. A lot of our product stack is built on the OSM data set, so we have a vested interest in improving it wherever we can. We do a whole bunch of analysis to try to identify areas with errors and shortcomings.
We built and use this tool:
http://osmlab.github.io/to-fix/
to queue up stuff that needs fixing, and we have people churning through it all the time.There are some really cool things in mapping tech. For example, Strava has made available a whole dump of point data that can be used to look for un-labelled trails and roads (see the "Strava" layer in to-fix).