I bought my wife a GPS abecause she has a hard time reading maps and planning routes, and it has been helpful for her. My sons inherited her map reading skills, not mine, so I ended up buying GPS units for them when they started driving. Me? I read maps just fine, and I used my biking GPS occasionally when I was traveling away from home. That all changed after a trip to Raleigh. I had printed directions to the hotel that were quite accurate but they were complex enough that I could not remember the whole route.
Once I got to Raleigh I found myself paying too much attention to the directions and not enough to the traffic and the signs. I did not have any adverse outcomes, but that weekend convinced me a GPS is extremely useful for navigating in unfamiliar cities even for people like me who are not directionally challenged. My biking GPS is not quite useful because it just beeps when there is an upcoming turn, so I still have to break my concentration on traffic and signs. I went ahead and got myself a Garmin that talks to me. I don't use it much but when I want to go anywhere unfamiliar it is wonderfully useful.
Of course, anybody who uses a GPS without paying attention to the roads and where they are at is dangerous, just as any other inattentive driver is dangerous. Also, I almost-always still carry a map (and written directions for unfamiliar destinations) even though I have the GPS. I guess I'm sometimes a belt AND suspenders guy.