I've said this before but I'll say it here once more. We already know that the way your movements are tracked is not the greatest in the world. However, there are limitations involved here, both with the nature of web browsing and with hardware/software expense. Being able to accurately track what forums/threads/and posts have been read/not read by every single user is not easy at all. I mean, think about how many sites you visit that track what pages you've been to, what articles you've read, and what new content has been added since your last visit. I think it's safe to say that 99% of all sites out there don't even bother (not even the biggest sites on the web ) primarily because of the complexity and costs involved.
If you come across a site that does a good job tracking your movements and accurately indicating what you've read and not read, I'll be more than happy to take a look at it so we can get a feel for what they are doing and more importantly, how they are doing it.