canuckseo - 12:15 am on Nov 21, 2012 (gmt 0)
My site had the same hit but the week before. on nov 16/17 it took a big jump up back to near where it was.
Also had a big hit for one site on Nov 16/17
I did a test - reoptimized 1 page that took a big hit. It was ranking top 3 for months before Nov 9 for a term in the body of the text but not in the title or description. After nov 16/17 it never fully recovered - got has high as middle of page 2. I reoptimized the page on the 19th to include the missing phrase in the title and meta description and now it's back to where it was. Coincidence?