gistfile1.php

<?php
function apci_groups_favorite_settings_form(&$form_state) {
  $default_option = FALSE;

  $form['options'] = array(
    '#title' => t('Favorite'),
    '#type' => 'checkbox',
    '#default_value' => $default_option,
  );

  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => t('Save'),
  );

  return $form;
}

function apci_groups_favorite_settings_form_submit($form, &$form_state) {
  global $user;
  // Get our current group.
  $group = og_get_group_context()->nid;

  if (is_array($user->top_groups)) {
    $group_nids = $user->top_groups; 
  } 
  else {
    $group_nids = array();
  }
  if ($form_state['values']['options']) {
    $group_nids[$group] = $group; 
  } 
  else {
    unset($group_nids[$group]);
  }
  drupal_set_message(t('Your form has been saved.'));
  user_save($user, array('top_groups' => $group_nids));

}
?>