How to create a dashboard widget for one user

You have to wait for wp_loaded to use get_current_user_id().

Example:

add_action( 'wp_loaded', 'wpse_80061_load_dashboard_widget' );

function wpse_80061_load_dashboard_widget()
{
    if ( 1 === get_current_user_id() )
        add_action( 'wp_dashboard_setup', 'wpse_80061_add_dashboard_widget' );
        // your function:
        // add_action( 'wp_dashboard_setup', 'my_catdb_setup' );
}

function wpse_80061_add_dashboard_widget()
{
    wp_add_dashboard_widget(
        'wpse_80061_widget',
        'Hey!',
        'wpse_80061_render_dashboard_widget'
    );
}

function wpse_80061_render_dashboard_widget()
{
    echo 'hey!';
}

For a dashboard widget with more details see my plugin T5 Table size dashboard widget.