I want to remove (or at least hide) the Preview button on some of my pagetypes, because those pagetypes are only viewable within their parent pages. Thus the preview will fail and looks terrible at the front-end :-)

Found this, but doesn't worked:

public function EditForm() {
		$form = parent::EditForm();
		$actions = $form->Actions();
		$actions->removeByName('Preview'); // remove save button from form
		return $form;
	}
	function getCMSActions(){
	    $actions = parent::getCMSActions();
	    $Action = new FormAction(
	           "doAction",
	           "Do something different"
	        );
	    $actions->push($Action);
	    $actions->removeByName('Save');
	    $actions->removeByName('Unpublish');
	    $actions->removeByName('Publish');
	    $actions->removeByName('Delete');
	    $actions->removeByName('Preview');
	    return $actions;
	}

I also need a solution to this problem, did you ever find anything?

I'm amazed there isn't a simple $allow_preview static for disabling it all together on certain page types.

No, unfortunately I found nothing about it, but I stopped working with SS completely :-)