The ? ? ? example is readable when you're inserting three values; it becomes really really easy to leave off, or add on an extra, argument when you're inserting fifteen or fifty values.

Think fast: is everything in the code below correct? I've already forgotten whether I've added an extra ? or left one off, and I just typed this 30 seconds ago.

    $sth = $dbh->("INSERT INTO a_table (lorem, ipsum, dolor, sit, amet, consectetur, adipiscing, elit, donec, malesuada, purus, et, tellus, dignissim, tristique, in, ipsum, neque, ultricies, quis, hendrerit, ac, pulvinar, eget, enim)
    ) values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?);");
    $sth->execute(array($lorem, $ipsum, $dolor, $sit, $amet, $consectetur, $adipiscing, $elit, $donec, $malesuada, $purus, $et, $tellus, $dignissim, $tristique, $in, $ipsum, $neque, $ultricies, $quis, $hendrerit, $ac, $pulvinar, $enim, $eget));