danny - 1:43 am on Feb 9, 2005 (gmt 0)

Here are the figures for referrals from www.google.com/search for my biggest site since the update, as percentages of the January average:

February 3: 21%
February 4: 13%
February 5: 9%
February 6: 14%
February 7: 19%

There's nothing even remotely blackhat about my site. It's static HTML with no frills - no Javascript, not even any images - except for AdSense. It has huge numbers of (almost entirely unsolicited) incoming links, from all over the place, and almost no SEO has been done on it (page titles are derived from book titles).

The only thing I can think of is that my AdSense alternate ads are causing a problem. For a while I had myself convinced that was the explanation, but the more I think about it the more implausible that seems.