Multiple Ideas

GeoPoke

Think Facebook Poke, but with location. This is an iPhone app where a user can 'poke' their friends, essentially asking them for their location. The person who 'pokes' also discloses their location in the process.

Geo Vacation Planner

This web/mobile app can plan your vacation itinerary for you. When I plan a vacation for an unfamiliar city, I start knowing only how many days I budgeted to spend there. Since each point of interest has a location, hours of the day open, and length of time required. The algorithm can take these into consideration when planning an efficient and enjoyable itinerary. It can also take into account your schedule and preferences.