estiating time till next turn

FWIW Kim's software already does this. Some of the screens tell you how many meters until your next turn and some of the voice prompts will tell you an estimated time of arrival.

Anyway, I am certain that at least speed and mileage would be available through OBD-II, and I think that those would be useful for a navigation software.

You can get speed directly from the GPS and it seems to be quite accurate (my GPS shows speed that is accurate enough that I can not tell if there is a difference between it and my speedo).

Anyway, it may be useful as a double check, but I wonder how much it would really help.

-Mike