With the recent long threads on MTD for IT I've been frustrated again with the inability to properly follow long threads.
Generally, when dipping back in to a thread you've visited before, the posts you haven't seen are highlighted. If the thread has more than one page of responses though, visiting the first page clears the highlights from subsequent pages, meaning when you get to the recent posts there's no distinction between what you've seen and what you haven't.
Usually at that point I give up. It would be good if we could either get rid of pages altogether or have highlights persist when you flick forward through the pages of responses, either way, having them disappear before you've seen them is useless.