When clicking a thread you have already viewed, perhaps you could be taken to the first post in that thread that you have not read.

Currently I have to click the thread, and then skim to the end, and back up to find where I hadn't read up until.

Perhaps I am missing a setting for this, or something, but alas, I cannot see that it's possible.

A minor point, but a massive improvement in usability.

Another point to consider would be allowing people to make use of the "block" feature that I know is built into vBulletin, being able to ignore certain peoples post would certainly make the forum a more pleasurable place to be.