Don't use tables for a lists of things in forms

Tables in the case form are semantically incorrect.

The assignment table also causes the need for fiddled in the theme function for #464834: Permission to assign case to account for access.

Use floats instead maybe? Perhaps either code or CSS from theme_links?

    $header = array_fill(0, 5, array());
    $header[0] = $form['assign_to']['#title'];
    $radios = array();
    foreach (element_children($form['assign_to']) as $id) {
      $radios[] = drupal_render($form['assign_to'][$id]);
    }
    $radios = array_chunk($radios, 5);
    $output .= theme('table', $header, $radios, array('class' => 'casetracker-assign-to'));
    drupal_render($form['assign_to']);