well i myself (as well as others) have been getting irritated with the way vbulletin decides what posts are new and which have been read...
before it was cookie based...
which also meant if you were idle in the forums for like 15mins or so.. it marked all new posts as being read..
i changed this, and now you should have to actually read it for it to be marked a read..
BUT
changing this means most (if not all) posts are marked as new...
so on the main forum page, towards the bottom you should see "mark forums read" and that will mark everything read for you...
sorry bout this, but it will be much better then the old method