I've been browsing the forum for the last couple of days without frames - just the main frame taking up the whole window. Works nicely, except that this morning I stopped getting my list of unread posts updated. Every time I reloaded the forum index, new posts would appear, but the were already marked read! Uh oh, is Tom mucking with the forum code again?

Nah. Stupid me, I had clicked on the big [Mark all as read] link and was then reloading that. Duh.

Even better is that it was I who requested to have a global Mark-all-as-read in addition to the ones for the individual forums. Careful what you ask for!
I dont know bout you, but ive never clicked mark all as read, and more often than not Ill get posts ive never clicked on marked as read. I really hate it cuz i dont know what i havent read.
In response to Jotdaniel
Ah, that's because the forum currently only saves the last 100 unread posts per forum. So if you go a few days or more without reading some of the busier forums, the older posts you haven't seen will be pushed off the unread list already.

I generally scan the list of topics in each forum, click on the ones that sound interesting, and then Mark all as read to clear the rest. Saves a lot of time!