Rxを使って、LocationChangedイベントを捕まえる --泣きながらC# ref: http://qiita.com/items/e9f61340f3de7698c804

rxgps.cs

var geoWatcher = new GeoCoordinateWatcher();

Observable.FromEvent<GeoPositionChangedEventArgs<GeoCoordinate>>(geoWatcher, "PositionChanged").
ObserveOnDispatcher().
Select(ev => ev.EventArgs.Position.Location).
Take(1).
Subscribe(location => Debug.WriteLine(location.Longitude.ToString()), () => { Debug.WriteLine("completed"); geoWatcher.Stop(); });

geoWatcher.Start();