Randall Munroe's xkcd #201 suggests "Let's take our latitude & longitude, put our birthdays after the decimal points, then go to that spot and make out." Clearly, the world needs this as an Android app.
- Respect local date format.
- Add alternate spots in case the originals are not reachable (over water, etc). Uses "ceil(lat,lon)-birthdays" as opposed to the normal "floor(lat,lon)+birthdays".
- Remember birthdays across app restarts.