Marshall's proposed problem is just one of many. This may not be a financial success at the moment, but it looks like a forward thinking startup with a core technology that has the potential to be very influential in your daily life. Think about all the things you do each and every day in which your location is a key (independent? not a mathematician) variable. When <here> do x, when <there> do y. I think geoloqi's own homepage[1] has some pretty interesting use cases (under uses).
[1] - http://geoloqi.com/