There is a drop down list at the bottom of each forum saying, "Show" and then a number of options - you can display threads that have been active "within the last week" and therefore, showing only the most active threads rather than ones that were posted to, say, 3 months ago. You can also change the default display for this in the 'My Home' section.
Click on 'My Home' and go to "Display preferences, number of shown threads, languages, colors..." and it can be changed there.
Regards,
