For all of its awesome applications, GPS has two fundamental flaws: It doesn't work indoors, and it can't really detect altitude. An Indoor Positioning System would fix that -- and introduce some seriously awesome applications.
Geolocation was listed as one of the important growth industries for the future (it also is a way to reassure students that the their are jobs for geography majors). The IPS isn't quite here, but it's hard to imagine that is too far away.
Via Seth Dixon