I've been playing with it for 2 or 3 months now, and i found it to be the best opensource navigation system out there. I even used it recently for my holidays.
The main branch isn't too updated, but the guys are working on what they call the 'modular map' branch, which is early beta yet but will integrate more flexible data sources (like openstreetmaps).
There's also a work in progress for a SDL interface :
The plugin system got fixed recently, and you can now read POIs from mdb files or asc / csv.
The GUI needs some more work, but it's being working on, and with more people involved, things will grow faster!
If you're interested and need some help, feel free to contact me :)
It would be great to get some help of people frome OSM for importing / exporting maps to/from navit..
(i forgot to subscribe to mail notifications, hence my delayed answer ;) )