Salut!
I’m also working on OSM → MP converter 
Current version supports multipolygons and routing (pseudo, without turn restrictions).
You can download it here: http://garminmapsearch.com/osm/osm2mp_v04.zip
It’s still in early phase, sorry for dirty code
Usage: osm2mp.pl file.osm > result.mp
Some examples, updated daily: http://garminmapsearch.com/osm/mp/
Main discussion in Russian: http://forum.openstreetmap.org/viewtopic.php?id=694
It was tested with up to 2GB .osm files from http://download.geofabrik.de/osm/europe