MKMapView zoom to users location on viewDidLoad?

did you set showsUserLocation = YES? MKMapView won’t update the location if it is set to NO. So make sure of that.

It is very likely that the MKMapView object doesn’t have the user location yet. To do right, you should adopt MKMapViewDelegate protocol and implement mapView:didUpdateUserLocation:

map.delegate = self;

...
-(void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation 
{
    MKCoordinateRegion mapRegion;   
    mapRegion.center = mapView.userLocation.coordinate;
    mapRegion.span.latitudeDelta = 0.2;
    mapRegion.span.longitudeDelta = 0.2;

    [mapView setRegion:mapRegion animated: YES];
}