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.