Sat-Nav (or GPS) makes you stupid. Best of all, you don't even need to be in a car to be stupid.
A couple of months ago, I moved house. Having DIY to do hasn't been very conducive to cycling to work, so I haven't managed to do it for about 3 months. During that time, almost every vehicular journey away from the house has been in a car, with a (very lovely) Tom Tom GPS.
I have now lost my ability to travel even short distances on my own. I took my dad to the station (about a 20 minute drive) sans-GPS the other day, and went the wrong way. A couple of weeks ago, I rode my bike to a nearby shop and went the wrong way. Today, I went the wrong way to work.
I swear it's because what previously required a small amount of due care and attention has not needed any. I just get in the car, and it tells me where to go. Sadly, the bike isn't that clever, and the consequences of going the wrong way require considerably more effort on my part to put right.