Cat,
You're right - a board that has had no activity for more than 30 days will show up with the blue light icon. This is particularly noticeable on the rarely used boards like Reproduction Parts and the Model Cars one. From the last post entry it is easy to see if any of the boards are suffering this regression, before going into them.
The cure when it starts to occur is to read everything (or at least everything in the boards in which you have an interest), and then on the front page click the "Mark ALL Posts As Read" button. This resets the flags for all threads on all boards. If you've already gone into a board and discovered that there aren't any new posts after all, click the "Mark Topics As Read" button. This has the same effect, but only for that board, obviously.
And as a general aside, I find using a browser that supports "Tabbed Browsing" (ie not Internet Exploiter) makes using this forum a breeze and pretty much renders the Last 10 Posts link redundant. I use Safari (for MacOSX), but
Mozilla's Firefox (available for PC and Mac) also has this feature, as do others. Browsers other than IE are also far more secure from viruses, Trojans and other nasties that plague the PC platform. Security in IE is a bad joke, it's about as solid on that front as a colander made of swiss cheese.
Anyway, getting back to using Tabs for browsing the forum. You open the main forum page, and then open each of the boards that show new posts in a new Tab. Then in each Tab you simply start at the oldest topic with a new post, and click "Newer Topic" to progress forward to the latest post. This approach gives you only the recent stuff, but with each post's full context.
cheers
RET