Add tags to AlertView

gistfile1.m

// Crear alerta, asignar delegate y tag
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" 
                                                        message:@"You must register a Facebook account first" 
                                                       delegate:self 
                                              cancelButtonTitle:@"Cancel" 
                                              otherButtonTitles:@"OK"];
alert.tag = 101;
[alert show];
[alert release];

// Verificar tag en el metodo del delegate
#pragma mark - UIAlertViewDelegate
-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
    switch (alertView.tag) { // comparar tag
        case 1:
            break;
        case 101:
            break;
        default: // Ejecutar esto cuando NO se asigno ningun tag
            break;
    }
}