If you use the Show unread posts since last visit facility which appears at the top of the forum page, there is a MARK ALL MESSAGES AS READ button which you can press once you have scanned down the list of unread items, read the items you want to read then you can press this button which will clear all unread items listed on the forum pages. Hope that helps.
Didnt know that - will try it!
Does that work if you are always logged in somewhere (usually my home machine is on and has a browser with coffeeshop open and logged in on)