Seems to be a lot better now. Newer versions of vBulletin have a sorta schizo way of handling it; not the most perfect way (such as how Simple Machines Forum does it) but at least it sorta remembers that you haven't yet read some threads.
It's not quite auto-mark but if you use the "Forum Tools" drop down menu, there is a selection titled "Mark Forum Read" that does exactly what it says.
There is also a "Quick Links" feature that marks all forums read.
Not automatic by any means but the functions are there.
Kit (AKA Cranky Kong)
Total Flights/Impulse as BAR (2010): 74/11,019.58 Ns (Equivalent to an 8% N motor.)
2015 Year-to-date: 5/2,017.78 Ns (Equivalent to a 58% K motor.) "Runs with scissors, doesn't play well with others"