Pekka,
Thank you for the detailed answer. You've really built some amazing software with this forum, and I know I'm not the only person who appreciates both the work you've put into the software but also that you provide this place for the community of photographers to share their work, exchange ideas and learn from each other. It is very much appreciated.
What I like about using the feature in the forum, for marking things unseen, is that it doesn't matter what browser I am using as long as I am logged in, I can get to the correct spot in the thread to continue reading. I have several browsers installed on my main computer, but also have a few computers I use as well as my phone to browse the forum. So using a bookmark to keep track of my location in a thread wouldn't be as useful as using the feature you have built. For my use case, I think it is actually easier to do exactly what you said, first unfollow the thread, then go to the location where I have gotten, and start following it again. Then I can use the traverse unseen to work my way through the thread, and collecting all the great tips and tricks other photographers have shared in this epic thread. Well, actually I have a few epic threads I'm following in this manner, it's just this one that I guess I originally clicked follow in the wrong spot.