Hmm. I have a subject field added from this download, but when I try changing the code in contact_us.php to this:

define('EMAIL_SUBJECT', 'Message about '. $subject);

...it doesn't work. Anyone have any ideas why not?

It is defined as $subject in tpl_contact_us_default.php:

<?php echo zen_draw_input_field('subject', $subject, ' size="40" id="subject"')