Is it just me, or does the forum have troubles marking postings unread properly when you're using multiple browsers/computers? It's really hard to predict which postings are marked unread when I log into Everypony.com. Sometimes I'm lucky enough to see everything posted since my last visit marked unread, sometimes nothing is marked at all after multiple days of absence, and I have to figure out where to start reading which is difficult considering the speed at which threads tend to grow. I've read somewhere that the read/unread status (or something like this) is stored in a cookie saved on your machine, so if you want this to work properly, you're stuck with one and the same browser on one and the same computer all the time. Me, on the other hoof, I switch between three or four computers, some of which can boot multiple operating systems, and two or three browsers per OS, so I can't even tell you which browser on which OS on which computer I used the last time I was here. Besides, this isn't the first vBulletin board I'm on, and I've never experienced this with vBulletin before.
Indeed, cookies are stored within the browser.. All I can suggest is clicking the navbar -> Mark Forums Read just before you log off everytime (and do 'log' off, don't just close the window). There is also an option to display all new posts (which I'm sure you've noticed) and in the options tab you can actually restrict the board showing you threads older than a specified time - So you'll only and always see the latest discussions.