RB gets round the "maximum number of tracks" problem that arises with the original firmware, if that's what you are asking (I think I have over 100,000 tracks on mine).
In my experience it still isn't entirely reliable for synching tracks in flash modded ipods, though, but you can copy files in the original firmware's disk mode, which avoids that issue. Also, building the database takes so long that I tend not to bother, and just use the file-browser and playlists.
Downside is, as you say you use it in the car, that an rockboxed ipod won't necessarily play well with every external device (that's Apple's doing, though, I think - many devices decide not to work if it's not recognised as an unmodified Ipod, and I gather there's some sort of stupid encryption involved)