FROM PERSONAL EXPERIENCE with the Nokia E90 reading me its maps and after more than 1000 miles using the Garmin Nuvi 360 to take me around places unmarked by signs or road stripes, I know how you need to balance the advice of a GPS. I have used GPS devices while driving, walking and cycling. You cannot depend on them unless you know how they think. And as several red top British newspapers report, you shouldn't think you'll get away with stupid driving just because you followed your GPS.
"In the UK, a ridiculous 300,000 car crashes have been caused by GPS. According to a survey commissioned by The Mirror, 1.5 million drivers have swerved through traffic when following their sat-nav's instructions a little too closely". Charlie Sorrel says, "The list of errors caused by slavishly obeying absurd commands would be hilarious if they weren't so dangerous: Driving onto a railway line, heading the wrong way down one-way streets, hurtling headlong into ditches, getting stuck under bridges and ignoring road signs."
Charlie Sorrel -- "GPS Causes 300,000 Brits to Crash" in Wired's blog, 22 July 2008.