theme_username($object) in Drupal 7?
That code has been moved in template_preprocess_username(), which is called before the theme function.

// Set the name to a formatted name that is safe for printing and
// that won't break tables by being too long. Keep an unshortened,
// unsanitized version, in case other preprocess functions want to implement
// their own shortening logic or add markup. If they do so, they must ensure
// that $variables['name'] is safe for printing.
$name = $variables['name_raw'] = format_username($account);
if (drupal_strlen($name) &gt; 20) {
  $name = drupal_substr($name, 0, 15) . '...';
}


If you need to use the full-length name, you should use $variables['name_raw'] in your implementation of theme_username(), remembering that the value has not been passed to any sanitization function.