Nice touch, defiantly not a bad idea. My only concern would be customers whom have Flash disabled or a previous version of the .swf's used on the product images. Are you doing a plugin detect to adjust to IMG tags incase? Another approach might be to use the GD library in PHP to generate JPG/GIF's instead, since they are more friendly. But nice none-the-less.
Here's the Macromedia Technote on passing local variables:
http://www.macromedia.com/support/flash/ts/documents/local_query.htm