Running Firefox on Ubuntu and with multiple forums open (tabbed browsing) if I mark one forum as read using Forum Tools, none of the others show bolds either though they have new unread posts. Also I just replied to a poll on the Communting forum and when I clicked back to Commuting by the drill down link at the top of the page all the unread bolds had dissappeared.

For the geeks: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.16) Gecko/20080715 Ubuntu/7.10 (gutsy) Firefox/2.0.0.16