Are there some technical issues affecting web traffic?

I occasionally check other blogs to see how they are doing for traffic. Most blogs use an open SiteMeter, as I do, so checking is easy. For example, I checked Brian Maloney's "The Radio Equalizer" blog, and his peak day of the last 30 days was also September 13, 2007. His peak was much higher than I have achieved, but the overall pattern is similar. Tom Maguire's JustOneMinute blog has a rather different pattern, although he too had a spike on September 13.