It’s a similar pattern to that for posts. The maximum rate for new threads pretty much coincides with the maximum rate for new posts, which was just before PTP.
I’ve also noted that time of day is now much more significant. Most of the activity now seems to occur during North American work hours, and less in the evenings. My recollection is that when I first started posting, there was a fair bit of posting in the evening, which is when I tend to be on-line. Now, there doesn’t seem to be much traffic after about 8 p.m., so threads don’t move much on the title pages.
But if I’m posting during the day and following threads, the traffic can be pretty active, with thread titles moving around a fair bit on the title pages.
If this suggests that most Dopers do their on-line stuff during work-hours, and extrapolate that to the North American workforce in general, we may have found the real cause of the economic slow-down. 
But how about the Dread Pirate Bob Marley? Huh?