Normally, new posts in sections are marked with orange. However, sometimes as i'm browsing, the orange will disappear and its harder to tell where there are posts I haven't gotten to yet. Any ideas?
Try to make sure you explicitly log out from one machine before logging into another.
I have had the same problem myself a few times, but when I have been left logged on at work, then come back home and logged on, then gone back to work still logged in (etc).