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If just we could get such detail about Panda
I may have crawled out from under the page layout problem but there may be other things. It looks like my site had smaller (10 to 20% drops) around July 2nd and August 19th. I'll have to corellate those to other algorithm changes.
Here's a useful quote from the Google blog article:
If you decide to update your page layout, the page layout algorithm will automatically reflect the changes as we re-crawl and process enough pages from your site to assess the changes. How long that takes will depend on several factors, including the number of pages on your site and how efficiently Googlebot can crawl the content. On a typical website, it can take several weeks for Googlebot to crawl and process enough pages to reflect layout changes on the site.
After the January 19th update, I read several accounts of people with images or flash in prominent positions above the fold that had no problem. It looks like Google is attempting to take content other than text into account, and getting somewhat better at it with this update.