Indeed. Data sources is the main concern.
Where to get navit :
There's the main branch, available from cvs. This will work only with datas like Falk's reiseplanner, as stated on the website.
There's the fork with the sdl gui. It's based upon the main branch, so it will need the same datas sources.
And, here comes the modular_map branch. It can use the datas of the two previous, plus garmin, plus openstreet maps. And it keeps growing
I'm currently porting the sdl gui to the modular map.
So basically : if you have falk's reiseplanner, or something compliant, you can use the branch and gui of your liking.
If you have garmin, or want openstreet maps, you need modular_map.
If you have issues getting datas from the CVS, i can roll a tarball and put it somewhere. But since i'm lazy, i'll only do it on request
(i believe there's tarballs of navit in the nghost forums. i'll post the link later).
I think the main branch is soon to be deprecated (hence its slow development), because the modular_map branch is starting to reach its goal. I'll let you know