There was a post in the WordPress.org support forums asking about the Google Maps shortcode used on WordPress.com sites. The feature is explained at http://en.support.wordpress.com/google-maps/

The user had decided to move from WordPress.com to a self hosted site and the Google Maps shortcodes had stopped working, leading to ugly text where the maps should have been. This plugin addresses this issue by implementing the shortcode.

To use, just activate the plugin. Existing posts using the shortcode will show up correctly again. New maps created by copying and pasting Google’s <iframe> code will be converted to use the shortcode.

Download Google Maps Shortcode Plugin