maybe it's because of the automated import (tiger for US and recently geobase for Canada) but the border is there 4 times at many place. I took a random place between Montana and Alberta ( osm.org/?lat=48.9952&lon=-110.647&zoom=14&layers=0B00FTF ) where I get those way:
osm.org/browse/way/15808114
osm.org/browse/way/30114504
osm.org/browse/way/24307864
osm.org/browse/way/16799216
so as I understand there is
one from national US border from tiger
one for the county border(source = county_import_v0.1_20080508235444)
one for the Alberta border from geobase
and finally one thats got almost everything (well except county) and as been make manually
to add to this there is almost 200 meter between the 2 farthest wich cause problem as some place (a street between theme...)
so what can we do about that, it more than 5000 km of border (and I didn't check the Alaska or any other border from US or Canada, but I looked in Europe and there haven't any problem like that?