Date select not rendering

Hi all,

I'm trying to use a 'date select' widget on a custom form, but not getting much output. Here is a snippet from my form creation function, which for testing is taken largely from the documentation sample:

  $date = time();
  $format = 'U';
  $form['start_date'] = array(
    '#type' => 'date_select', // types 'date_popup', 'date_text' and 'date_timezone' are also supported. See .inc file.
    '#title' => t('Date'),
    '#default_value' => $date, 
    '#date_format' => $format,
    '#date_label_position' => 'within', // See other available attributes and what they do in date_api_elements.inc
    '#date_timezone' => 'America/Chicago', // Optional, if your date has a timezone other than the site timezone.
    '#date_increment' => 15, // Optional, used by the date_select and date_popup elements to increment minutes and seconds.
    '#date_year_range' => '-3:+3', // Optional, used to set the year range (back 3 years and forward 3 years is the default).
    '#datepicker_options' => array(), // Optional, as of 7.x-2.6+, used to pass in additional parameters from the jQuery Datepicker widget.    
  );

This is largely abstract at this stage, but I'm just trying to get things working before I add real content etc.. The format of the default value and value I want returned is unix timestamp.

And the output this generates:

<div class="container-inline-date"><div class="form-item form-type-date-select form-item-start-date">
  <label for="edit-start-date">Date </label>
 <div class="date-padding clearfix" id="edit-start-date"></div>
</div>
</div>

Any help would be much appreciated.

Cheers,
Greg.