I notice alot of the same threads are created. So the first time an MBTI topic is created, such as 'ENFP + INTP = TEH AWESOME' or 'THE MAJESTIC AND WONDERFUL INFJ' it will get many replies. But after the 3rd exact same thread, they just sort of die.
This can cause a new group of posters who were interested in the topic to never get to participate and become part of the forums.
So while we are losing old members through natural processes such as swine flu, newer members aren't as quick to replace them and invest in the forums.