It definitely takes me longer. Pre-GPS, I might need a map (or at least notes) to get somewhere, but then I could most likely find my way back on my own. Using GPS to get somewhere, I'd be lost trying to get back without it.

I think that because with a map you are looking at street signs/names, etc. both in advance to plan the route, and much more actively and intently while driving to figure out "do I turn here" and you just remember that stuff. Where as a GPS says "turn right at the next light" and you really don't remember any context around that.