I use Google Reader to read a large number of blogs and other RSS feeds. It displays charts of the number of posts I've read in each day of the last thirty, and also the number of posts I've read in each hour of the day and day of the week over a 30-day period.
There's pronounced periodicity in the number of posts read on each day, which comes from periodicity in posting frequency (I probably read blogs twice a day or so). In particular certain days of the week see more posts than others -- in most weeks I read the most posts on Wednesday; then Tuesday and Thursday; then Monday and Friday; then Saturday and Sunday. I've known this for a while.
But in the last thirty days, I have read more posts on Friday than any other day. The numbers are as follows: Sunday, 369; Monday, 636; Tuesday, 719; Wednesday, 784; Thursday, 724; Friday, 883; Saturday; 448.
Where are all these extra Friday posts coming from?
Well, it's Saturday. The last 30 days are a period going from a Friday (May 16) to a Saturday (June 14), including five Fridays and Saturdays and four of each other day.
If I consider the last twenty-eight days instead, I get 696 for Fridays and 378 for Saturdays, and the profile for the month looks like the profile for any given week.
But the fact that thirty isn't divisible by seven has an interestinng effect there.