I'm using Mapfactor on a UMPC and a phone for a very long time. It is my favorite navigation. However there is one thing that bothers me. Quite often Mapfactor sends me to a shorter but very disadvantageous route.
For example if a highway is curved to the right and there is a parking place, it navigates me through it, because it is a few meters shorter. This happens also on other locations and I can give you exact examples if you want to.
I think the solution to avoid this is quite simple. Penalize every crossroad especially if you are joining a different road and you have to yield. Crossroads with traffic lights may be penalized even more (make it an option). Avoid leaving current road and joining it again within ~1 km unless there is a very good reason to do this.