But I have seen it done. As we speak there are posts in the clip and image section right now that are bolded and others arent... In this very section I see the post "Trouble posting" bolded while the others are not.
That would be because those threads are new or have new posts in them since the last time your viewed that section. Try clicking on a bolded thread with only a few posts in it and then returning to the section index. Hit the F5 key and look at the title again. Is it still bolded? Once you read an updated thread it becomes unbolded, signifying that it has been read/viewed. This is an automatic thing.