Knowing what threads you've read

In most forums, you can tell which threads are new and which you've read.  Usually the thread has a different icon on it once you've read it.  The forums (like phpBB) also give you the ability to mark entire threads/categories as read. 

We have users that don't use email as much so they will keep up with the discussions on-line.  Therefore, they want to be able to more easily "visualize" what they haven't looked at yet.  Sort of like seeing unread email in your inbox.

Thanks,

Chris