I notice Walkhighlands are now using OSM data for the maps on their website. It looks like they are using OS OpenData for roads, placenames, contours etc, plus OSM for paths and tracks.
And the maps look quite nice - fairly similar to an OS Landranger.
See for example one of their walks: http://www.walkhighlands.co.uk/maps/map1_13cg.shtml
They also have a route planner, using the same maps: http://www.walkhighlands.co.uk/maps/