Remove toolbar option (and set to default to no) in user profile

To set the default to not show the admin bar on the public side at registration put the following in your theme’s functions.php file (note: this will only work for new users, you’ll have to manually disable it for all your current users via the Dashboard):

// Disable the user admin bar on public side on registration
add_action('user_register','trash_public_admin_bar');
function trash_public_admin_bar($user_ID) {
    update_user_meta( $user_ID, 'show_admin_bar_front', 'false' );
}