Version 2.5 of my related posts plugin for WordPress comes with the following changes.
Improved the AJAX search utility
Multiple widgets support
I have added support for multiple instances of the widget by using the new widgets API introduced in WordPress 2.8. You can now add the widget to all of your sidebars, or even multiple instances to one sidebar (for some obscure reason).
Fixed a bug where the widget wouldn’t show on pages
The widget would only be displayed in the sidebar for posts, not on pages. Fixed it.
Related private posts are now displayed to users who have the necessary priviliges
If you add related posts that are private to an item, logged in users with the necessary priviliges are now able to see them. Of course, the posts will not be displayed for users who do not have priviliges.