The update_form_enhancement module enhances update.php user interface by separating modules that are up to date from those that are not.
It uses standard form_alter hook to alter the form that is displayed on second step of update.php script to select modules that need to be updated.
Note about Drupal 7 and beyond: An equivalent feature implemented by this module is already in core, so the life time of this project dies with Drupal 6.
When all modules are up to date, a message is displayed for the site admin and the update form remains unchanged. The site admin can still reapply any update task should (s)he needs to.
When all modules have pending update tasks, a message is displayed for the site admin and the update form remains unchanged. This particular scenario may never happen, but anyway...
When some modules have pending updates and some are up to date, they are grouped into separated collapsible fieldset. The fieldset used to group modules with pending updates is displayed first and expanded, so site admins can easilly check what's pending. The fieldset used to group up to date modules is rendered last and collapsed.