tedster - 3:32 am on Sep 25, 2010 (gmt 0)
The only time I ever see wild fluctuations is when a new algo is brought online. It usually clears up after a few days or weeks.
I suggest you go now back and read drall's report a second time. He doesn't even see the fluctuations from an algo change that you do. No pattern changes at all, even for day of the week. And it's been like that for a very long time, while a PR 6 home page grew to a PR8.
Then read what he's seen happen recently with rankings when one of his pages gets a traffic spike because of social media activity. The other pages' rankings drop for the remainder of just that period, so that total traffic stays the same.
You can always choose not to believe it, but that report does not look like something accidental at work to me.