I'm currently working on C++ code to offer offline rendering of maps and also offer offline routing - both based on openstreetmap data. Currently the map drawing is reasonable good but still needs improvements (that should be simple to make but just needs some time). I will now start wokring on extracting the necessary data from openstreetmap to get routing done.

If anybody is interested to participate or use or integrate don't hesitate to contact me. My code is currently not as advanced as Navit but in my case maemo is the target #1.

Regarding Navit: It is difficult to extract city and especially street information from OSM, since at leats for germany the is no direct releation from the street to the "containing" city. The tagsa are there but they are not always used. Besides possible performance problems this might be the problem Navit may have.