In the People list, change from time span display to date display
I'm not aware of an existing module that will do this but the following function in a custom module will do the trick:

function MYMODULE_form_user_admin_account_alter(&amp;$form, &amp;$form_state) {
  // Get the user IDs listed in the form
  $uids = array_keys($form['accounts']['#options']);

  // Since loading the user objects will incur overhead it would be best to get the
  // created data directly from the users table. It's a shame because this query has
  // already been run in user_admin_account(), but it's not saved anywhere that we can
  // easily pick it up.
  $sql = 'SELECT uid, created FROM {users} WHERE uid IN (:uids)';
  $created_data = db_query($sql, array(':uids' =&gt; $uids))-&gt;fetchAllKeyed();

  // Loop through the results and change the column data for the "Member for" column.
  foreach ($created_data as $uid =&gt; $created) {
    $form['accounts']['#options'][$uid]['member_for'] = date('d/m/Y H:i', $created);
  }

  // Finally change the header to say "Member Since"
  $form['accounts']['#header']['member_for']['data'] = t('Member Since');
}


The only thing you might want to change is the date format...see PHP's date() function for all the available tokens