WP CommentWidgetizer is a simple widget that takes one of the approved comments made on any page or post of your site and displays it in the sidebar.
It can be used to manage guest books, or more simply to randomly export to your homepage comments spread deeper in your site pages in order to make it visible to your visitors not reaching the post or page holding those comments.
You can see the CommentWidgetizer widget used as guestbook homepage exporter here. French reading visitors will get additional insights on this widget genesis page.
This plugin is available for download to be used on your WordPress self-hosted installation.