NOT using the GPS will enlarge your brain!!!
It's what this paper from PNAS says: "Navigation-related structural change in the hippocampi of taxi drivers."
they are not kidding, PNAS stands for Proceeding of the National Academy of Science - so this is a serious paper... apparently they found out that a region of the ippocampus gets enlarged (and a close one shrinks to leave space for it) depending on the time the driver have been working in the london roads.
thanks to shelley at retrospectacle for this