Validate an ubercart checkout pane? I'm using the uc_ddate module. 

How would one hook into the checkout pane to cause it to force it to validate and make the delivery date option required?
Would that checkout pane still be captured by hook_alter_form()?  If so you could add #required to the field there. Let me have a quick try and I'll get back to you.

EDIT: OK, this worked for me:

function tools_utilities_form_alter(&amp;$form, $form_state, $form_id) {
  if ($form_id == 'uc_cart_checkout_form') {
    // Make delivery date required
   $form['panes']['ddate']['ddate']['#required'] = true;
 }
}


Create your own module (mine is called tools_utilities in this example) and implement the above and you should be good to go :)