gistfile1.php

<?php

/**
 * Jayj_I_Make_Themes
 *
 * Gets the theme readme from WordPress.org.
 *
 * Modified version of Mark Jaquith's I Make Plugins class
 * @link http://wordpress.org/plugins/i-make-plugins/
 */
class Jayj_I_Make_Themes {
	static $instance;

	var $readme;

	function __construct() {
		self::$instance = $this;
	}

	function get_theme_slug( $post ) {
		$post = get_post( $post );

		$postmeta_slug = get_post_meta( $post->ID, 'theme-slug', true );
		$slug = ( $postmeta_slug ) ? $postmeta_slug : $post->post_name;

		return $slug;
	}

	function get_theme_readme( $theme_id, $force_update = false ) {
		$slug = $this->get_theme_slug( $theme_id );

		if ( false == $slug ) {
			return;
		}

		if ( ! $force_update ) :
			// First, try in-memory cache
			if ( isset( $this->cache[$slug] ) )
				return $this->cache[$slug];

			// Next, try postmeta cache
			$ts = get_post_meta( $theme_id, '_theme_readme_timestamp', true );
			$rm = get_post_meta( $theme_id, '_theme_readme', true );

			// We force a dynamic update after 24 hours
			if ( $rm && $ts && $ts > time() - DAY_IN_SECONDS ) { // fresh
				$this->cache[$slug] = $rm;
				return $this->cache[$slug];
			}
		endif;

		// Fetch via API
		require_once( ABSPATH . '/wp-admin/includes/theme.php' );
		$readme = themes_api( 'theme_information', array( 'slug' => $slug ) );

		if ( is_wp_error( $readme ) ) {
			return false;
		}

		$this->cache[$slug] = $readme;

		update_post_meta( $theme_id, '_theme_readme', $readme );
		update_post_meta( $theme_id, '_theme_readme_timestamp', time() );

		return $readme;
	}
}

/*
$theme = new Jayj_I_Make_Themes;
$meta = $theme->get_theme_readme( get_the_ID() );
*/