We don't know for sure, but as people have suggested we assume it had something to do with the Tickled documentary. One morning I woke up and all those people were browsing around the forum and within a couple of hours they were gone.
Lol the Tickling convergence... There's a potential for a great story here. Or at least a Big Bang Theory episode title, haha
Just curious, how do you know? Are the forum statistics available, sorted by date? Can we see other types of statistics (male/female membership ratio)? Where can we see that? I saw a "statistic" tab at the bottom of the home page, but it is not accessible.
As far as stats (as Mark Twain said, there are liars, then there are statiticians...), I wonder how many joined on or shortly after that date? Not that they continued to parcipilate (intentional misspell).