Someone requested that I add functionality to my Drupal featured content block module to sort by the nodes that are the closest match to the node being viewed based on vocabulary terms. I did this, but then someone asked if I could integrate with views to allow for this same type of sorting. I thought maybe it could be done already, and sure enough, I was able to do it using views and the views group by module.

Make sure you are using a recent version of views (e.g. 6.x-2.8) and have installed & enabled the Views Group By module.

I've exported my view so you can play with it:

$view = new view;
$view->name = 'closest_match_by_terms';
$view->description = '';
$view->tag = '';
$view->view_php = '';
$view->base_table = 'node';
$view->is_cacheable = FALSE;
$view->api_version = 2;
$view->disabled = FALSE; /* Edit this to true to make a default view disabled initially */
$handler = $view->new_display('default', 'Defaults', 'default');
$handler->override_option('fields', array(
  'nid' => array(
    'label' => 'Nid',
    'alter' => array(
      'alter_text' => 0,
      'text' => '',
      'make_link' => 0,
      'path' => '',
      'link_class' => '',
      'alt' => '',
      'prefix' => '',
      'suffix' => '',
      'target' => '',
      'help' => '',
      'trim' => 0,
      'max_length' => '',
      'word_boundary' => 1,
      'ellipsis' => 1,
      'strip_tags' => 0,
      'html' => 0,
    ),
    'empty' => '',
    'hide_empty' => 0,
    'empty_zero' => 0,
    'link_to_node' => 0,
    'exclude' => 0,
    'id' => 'nid',
    'table' => 'node',
    'field' => 'nid',
    'relationship' => 'none',
  ),
  'title' => array(
    'label' => 'Title',
    'alter' => array(
      'alter_text' => 0,
      'text' => '',
      'make_link' => 0,
      'path' => '',
      'link_class' => '',
      'alt' => '',
      'prefix' => '',
      'suffix' => '',
      'target' => '',
      'help' => '',
      'trim' => 0,
      'max_length' => '',
      'word_boundary' => 1,
      'ellipsis' => 1,
      'strip_tags' => 0,
      'html' => 0,
    ),
    'empty' => '',
    'hide_empty' => 0,
    'empty_zero' => 0,
    'link_to_node' => 1,
    'exclude' => 0,
    'id' => 'title',
    'table' => 'node',
    'field' => 'title',
    'relationship' => 'none',
  ),
  'tid' => array(
    'label' => 'Term ID Count',
    'alter' => array(
      'alter_text' => 0,
      'text' => '',
      'make_link' => 0,
      'path' => '',
      'link_class' => '',
      'alt' => '',
      'prefix' => '',
      'suffix' => '',
      'target' => '',
      'help' => '',
      'trim' => 0,
      'max_length' => '',
      'word_boundary' => 1,
      'ellipsis' => 1,
      'strip_tags' => 0,
      'html' => 0,
    ),
    'empty' => '',
    'hide_empty' => 0,
    'empty_zero' => 0,
    'set_precision' => FALSE,
    'precision' => 0,
    'decimal' => '.',
    'separator' => ',',
    'prefix' => '',
    'suffix' => '',
    'exclude' => 0,
    'id' => 'tid',
    'table' => 'term_data',
    'field' => 'tid',
    'override' => array(
      'button' => 'Override',
    ),
    'relationship' => 'none',
  ),
  'views_sql_groupedfields' => array(
    'label' => 'Group By Fields',
    'alter' => array(
      'alter_text' => FALSE,
      'text' => '',
      'make_link' => FALSE,
      'path' => '',
      'alt' => '',
      'link_class' => '',
      'prefix' => '',
      'suffix' => '',
      'target' => '',
      'trim' => FALSE,
      'max_length' => '',
      'word_boundary' => TRUE,
      'ellipsis' => TRUE,
      'strip_tags' => FALSE,
      'html' => FALSE,
    ),
    'empty' => '',
    'hide_empty' => 0,
    'empty_zero' => 0,
    'exclude' => '1',
    'id' => 'views_sql_groupedfields',
    'table' => 'views_groupby',
    'field' => 'views_sql_groupedfields',
    'relationship' => 'none',
    'views_groupby_fields_to_group' => array(
      'nid' => 'nid',
    ),
    'views_groupby_sql_function' => 'count',
    'views_groupby_fields_to_aggregate' => array(
      'tid' => 'tid',
    ),
    'views_groupby_field_sortby' => 'tid',
    'views_groupby_sortby_direction' => 'desc',
    'override' => array(
      'button' => 'Override',
    ),
  ),
));
$handler->override_option('arguments', array(
  'tid' => array(
    'default_action' => 'default',
    'style_plugin' => 'default_summary',
    'style_options' => array(),
    'wildcard' => 'all',
    'wildcard_substitution' => 'All',
    'title' => '',
    'breadcrumb' => '',
    'default_argument_type' => 'php',
    'default_argument' => '',
    'validate_type' => 'none',
    'validate_fail' => 'not found',
    'break_phrase' => 1,
    'add_table' => 1,
    'require_value' => 0,
    'reduce_duplicates' => 0,
    'set_breadcrumb' => 0,
    'id' => 'tid',
    'table' => 'term_node',
    'field' => 'tid',
    'validate_user_argument_type' => 'uid',
    'validate_user_roles' => array(
      '2' => 0,
    ),
    'override' => array(
      'button' => 'Override',
    ),
    'relationship' => 'none',
    'default_options_div_prefix' => '',
    'default_argument_user' => 0,
    'default_argument_fixed' => '',
    'default_argument_php' => 'if (arg(0) == \'node\' && is_numeric(arg(1))) {
  $node = node_load(arg(1));
  if ($node->nid) {
    $terms = $node->taxonomy;
    if (! empty($terms)) {
      $tids = array();
      foreach ($terms as $term_data) {
         $tids[] = $term_data->tid;
      }
      return implode(\'+\', $tids);
    }
  }
}
 ',
    'validate_argument_node_type' => array(
      'webform' => 0,
      'forum' => 0,
      'page' => 0,
      'story' => 0,
    ),
    'validate_argument_node_access' => 0,
    'validate_argument_nid_type' => 'nid',
    'validate_argument_vocabulary' => array(
      '1' => 0,
      '3' => 0,
      '2' => 0,
    ),
    'validate_argument_type' => 'tid',
    'validate_argument_transform' => 0,
    'validate_user_restrict_roles' => 0,
    'validate_argument_php' => '',
  ),
));
$handler->override_option('access', array(
  'type' => 'none',
));
$handler->override_option('cache', array(
  'type' => 'none',
));
$handler->override_option('distinct', 1);
$handler->override_option('style_plugin', 'table');
$handler->override_option('style_options', array(
  'grouping' => '',
  'override' => 1,
  'sticky' => 0,
  'order' => 'asc',
  'columns' => array(
    'nid' => 'nid',
    'name_1' => 'name_1',
    'title' => 'title',
    'views_sql_groupedfields' => 'views_sql_groupedfields',
  ),
  'info' => array(
    'nid' => array(
      'sortable' => 0,
      'separator' => '',
    ),
    'name_1' => array(
      'sortable' => 0,
      'separator' => '',
    ),
    'title' => array(
      'sortable' => 0,
      'separator' => '',
    ),
    'views_sql_groupedfields' => array(
      'separator' => '',
    ),
  ),
  'default' => '-1',
));
$handler = $view->new_display('block', 'Block', 'block_1');
$handler->override_option('block_description', '');
$handler->override_option('block_caching', -1);

Have fun!