Unfortunately it looks like Pinterest has changed their image server address and it is not reflected in the RSS feed. The RSS feed gives /upload/IMAGE FILE NAME.jpg as the image source, which translates to http://pinterest.com/YOUR_USER_NAME/upload/IMAGE_FILE_NAME.jpg. But now the images are actually stored at http://media-cache(NUMBER_1-?).pinterest.com/upload/IMAGE_FILE_NAME.jpg and the tricky part is that the number that goes in the parentheses in media-cache(NUMBER 1-?) is not consistent, so I will have to figure out how to determine what that number is. Ugh.
I will let you know as soon as I have time to figure it out. In the meantime, it looks like the plugin will not work for anyone.
If anyone has suggestions or knowledge of how to work around this, please post a comment to this thread.