The problem is poor routing more so than actual map errors. Yeah, there are plenty of map errors but they appear in the paper ones too. But when selecting my own route via a map, I make value judgments about the roads I choose. I know I'm driving a big rig and generally avoid the smaller roads and congested areas. And since I looked at the map myself and noted the actual roads I would be using, I generally know right away when things begin to go wrong. Not so when I am blindly following Ms Garmins directions and she suddenly wants to take a turn off a perfectly good road and try out some shortcut she has dreamed up.
I guess I should be impressed that the computerized routings work at all, but I've been lead astray too many times.