Add arbitrary classes to a Bean block.

preprocess_beans.php

<?php
/**
 * Implements hook_preprocess_block().
 *
 * Adds a few helpful theming classes to a bean block:
 * The bean's view mode, bundle (bean type), and the value of an arbitrary
 * field, 'field_image_size'. Use this for beans placed using core blocks or
 * the Context module.
 */
function THEME_preprocess_block(&$variables) {
  $block = $variables['block'];
  $block_module = $block->module;
  $elements = $variables['elements'];

  if (!empty($block_module) && ($block_module == 'bean')) {
    // The location of the Bean array within $variables is a moving target
    // E.g. use of the Context Module will change it's location to within
    // $elements['content']. Try the likely locations.
    if (array_key_exists('bean', $elements)) {
      $bean_array = $elements['bean'];
    }
    else if (isset($elements['content']) && array_key_exists('bean', $elements['content'])) {
      $bean_array = $elements['content']['bean'];
    }
     else {
      $bean_array = FALSE;
    }
    // Test that the Bean array has been found.
    if ($bean_array) {
      $mystery_key_array = element_children($bean_array);
      if ($mystery_key_array) {
        $bean = $bean_array[$mystery_key_array[0]];
        // Add bean type and view mode as classes to the block.
        if (isset($bean['#entity']->data['view_mode'])) {
          $variables['attributes_array']['class'][] = str_replace('_', '-', $bean['#entity']->data['view_mode']);
          $variables['attributes_array']['class'][] = str_replace('_', '-', $bean['#bundle']);
        }

        // Add an image-size class.
        if (isset($bean['#entity']->field_image_size[LANGUAGE_NONE][0]['value'])) {
          $variables['attributes_array']['class'][] = str_replace('_', '-', $bean['#entity']->field_image_size[LANGUAGE_NONE][0]['value']);
        }
      }
    }
  }
}

/**
 * Preprocess logic for Panels panes.
 * 
 * Adds a bean's bundle name as a class.
 */
function rTHEME_preprocess_panels_pane(&$vars) {
  if (array_key_exists('bean', $vars['content'])) {
    $bean_array = $vars['content']['bean'];
    if ($bean_array) {
      $mystery_key_array = element_children($bean_array);
      if ($mystery_key_array) {
        $bean = $bean_array[$mystery_key_array[0]];
        // Add bean type and view mode as classes to the block.
        if (isset($bean['#entity']->data['view_mode'])) {
          $vars['attributes_array']['class'][] = str_replace('_', '-', $bean['#entity']->data['view_mode']);
          $vars['attributes_array']['class'][] = str_replace('_', '-', $bean['#bundle']);
        }
      }
    }
  }
}

@jessehs does the 'variables'variable on line 12 need to be changed to anything?