Show updated & new status on issues and forum threads
It would be nice if Redmine kept track of the timestamp when you last looked at a thread or issue. Then, when showing lists of issues or threads (eg. the Issues and Forums) pages it could annotate the title with an "updated" or "new" tag to show which issues/threads have been updated or created since you last looked at them.
An example of this feature is provided by Drupal. If you have an account and go to http://drupal.org/project/issues/views you can see which items are new and updated (to see the updated tag you need to look at an issue and wait for someone to update it). Drupal also shows the number of new posts and when you click on that link it opens the issue at the first new post. It also tags the new posts with a new keyword to indicate which ones are new.
I've attached screenshots to illustrate the two concepts.