idea for proper compability with multiple values fields

actually you would add checkbox field to each set of fields in multigroup.

this function in custom module does the trick. Maybe it is possible to improve this so it could be a candidate for CCK Private Fields module?

Following code works if in multigroup a field field_privacy_profile_position is placed and one of options is 'Follower'. It is possible to hide field field_profile_position from people who are not followers.

function MODULENAME_preprocess_content_field(&$variables) {
	// Check if we are dealing with field that is protected and is about to be rendered in teaser or page.
	if ($variables['field_name'] == 'field_profile_position' && ($variables['teaser'] || $variables['page'])) {
		foreach($variables['items'] as $key => $item) {
			// Find delta.
			$delta = $item['#delta'];
			// Check settings of access field for that delta.
			if($variables['element']['#node']->field_privacy_profile_position[$delta]['value'] == 'Followers') {
				// Insert check if user is one in f. ex. follower category.
				$variables['items'][$key]['view'] = 'Insert access denied tokenized message here...';
			}
		}
	}
}

Markus, do you think such approach could be used? Is it safe enough to do things like this in preprocess function?

here are updated function that properly removes field from display without messages or leaving trace, messages will probably just encourage hacking :)

function MODULENAME_preprocess_content_field(&$variables) {
	// Array with privacy field and protected fields.
	// This could be sniffed out from $variables['element']['#node'] and
	// no manual labour would be required. Just look for group with field that
	// ends with _privacy and you get privacy field and the rest of fields are
	// protected.
	$fields['field_profile_contact_privacy'] = array(
		'field_profile_contact_value',
		'field_profile_contact_label',
		'field_profile_contact_type',
	);
	foreach($fields as $privacy_field => $protected_fields) {
		// Check if we are dealing with field that is protected and is about to be rendered in teaser or page.
		if (in_array($variables['field_name'], $protected_fields) && ($variables['teaser'] || $variables['page'])) {
			foreach($variables['items'] as $key => $item) {
				$delta = $item['#delta'];
				$roles = og_user_roles_get_roles_by_group($variables['element']['#node']->nid, $GLOBALS['user']->uid);
				$allowed = $variables['element']['#node']->{$privacy_field}[$delta]['value'];
				if ($allowed != 'Followers') { // Some test check.
					$variables['field_empty'] = TRUE;
				}
			}
		}
	}
}