pteam - 7:39 pm on Nov 5, 2012 (gmt 0)
I agree with Nichitia with:
"1. Possible excessive internal anchor links (in the case of one of the affected sites); "
I just had a site take a -950 penalty and I'm almost positive its because of internal linking. The site is only like 4 months old and just dropped all its rankings overnight. It has about 20 pages in total on the site. On the menu on the left we had on each page a few of the pages linked between each other but then overnight we decided to link all the pages between each other. I think this sudden addition of internal links caused the overoptimization penalty. You wouldnt think it would because its simple navigation of the site: links to your other pages for the browsers/users of the site to goto other pages that might interest them. We are going to remove like 50% of the links and some extra keywords on the page and see where it gets us.