Cloudmade's OSM Error Edition maps of the Isle of Man
This map of the Isle of Man is based on data from the OpenStreetMap Project. The focus of this set of maps is to draw attention to areas that still need development (e.g. missing road names), for this reason it is also not routable, nor does it come with a Mapsource or Roadtrip installer. If you are interested in contributing to OpenStreetMap then this map might be quite helpful, if not then there are better maps out there that you should use.
OpenStreetMap works that way, that everybody can upload their GPS tracks from which maps from all over the world are being created. This means that the quality of the map depends on the tracks uploaded by the users (you're welcome to contribute to the project by uploading your tracks as well) and therefore the quality differs greatly from country to country, region to region and city to city. As there are continuously new tracks being contributed the maps are getting better and better every day, so if a map of a region is not as detailed as you had expected either join the community and help by contributing and/or come back in a few weeks or months and you will most likely find a better map with more data and information than there was before.