The 'Member for' extra field has moved one level up in the array.
function user_update_8000() {
$settings = field_bundle_settings('user', 'user');
if (isset($settings['extra_fields']['display']['summary'])) {
$settings['extra_fields']['display']['member_for'] = $settings['extra_fields']['display']['summary'];
unset($settings['extra_fields']['display']['summary']);
field_bundle_settings('user', 'user', $settings);
}
}