One behavior of the old version that I liked, that this new version doesn't seem to follow, is the clearing of old threads that I've intentionally skipped.
That is, when I visited the forum, I'd run down the list of newly updated threads and click on the ones that interested me. After I'd leave the forum and come back a bit later, ALL of the threads from that previous visit (including the ones I didn't care to read) would be cleared (marked as read). I liked this. It made clearer the things that were newly posted since my last visit, rather than scanning through and keeping a closer eye out for the first thread down the list that's not in bold to tell me where I left off before. If I want that same behavior now, however, I'll need to click "mark forum read" after each time I read the threads I'm interested in. Not difficult, but not
as convenient as before.
I may be the only person who cared about this behavior though...