Custom layout with conditional stylesheets

Fantastic!
I shall use preprocess for now, but as you said, it would be nice if these could be handled.
As this would then keep relevant "code" all in one place.

EDIT:
For anyone interested here is the preprocess code I added.

function THEME_preprocess_node(&$variables, $hook) {
  // Optionally, run node-type-specific preprocess functions, like
  // THEME_preprocess_node_page() or THEME_preprocess_node_story().
  $function = __FUNCTION__ . '_' . $variables['node']->type;
  if (function_exists($function)) {
    $function($variables, $hook);
  }
}

function THEME_preprocess_node_panel(&$variables, $hook) {
  $display = panels_load_display($variables['panels_node']['did']);
  $layout = panels_get_layout($display->layout);
  $data = $layout['path'] . '/' . $layout['name'] . '-ie.css';
  $options = array(
    'browsers' => array(
      '!IE' => FALSE,
    ),
  );
  drupal_add_css($data, $options);
}