Currenlty, destination signs are already shown appr. 2km ahead. This is great for highways, where the speed is appr 120 km/h/ 100km/h For secondary roads, and even within city limits, this sdistance is way to far ahead. The destination signs are sometimes shoown when still several turns have to be made. This is confusing. Can the destination signs made dependent on road type or max speed on the road. Without any scientfic backing, I would say that for 80 km/h roads, a nicer distance would be 400m, within city limits, 200m would suffice.
They are defined on the road directly after the point where the sign is located, see http://wiki.openstreetmap.org/wiki/Key:destination. Mapfactor shows them before you reach that point, so you can anticipate on the direction to take. It does so some 2km ahead. For destination signs on non-highways this is too early.