chrisv1963 - 4:46 pm on Mar 8, 2011 (gmt 0)
I had a very close look at pages that lost rankings and it looks like the new update has a problem with pages with pictures and a small amount of text.
My website about "widgets" has thousands of pictures of widgets and used to rank on the first page for "widgets". This was logical because people come to the website to view pictures of widgets and share them on Twitter, Facebook, ... Now it is on the 4th page for that keyword. I have hundreds of pages with thumbnail galleries (+ some text to explain what that collection is about) and each thumbnail links to a page with the full size image of the widget + text (between 50 and 200 words). Google might see this as thin content.
Unfortunately, through my breadcrumbs, each page with a thumbnail gallery and each page with a full size image is linking back to the main pictures index page, using the anchor text "widgets". My guess is that Google thinks I'm trying to cheat because I'm linking back all the time from "thin content" with that anchor text. As a result I ended up on the 4th page.
I have many exellent rankings on the first page of the serps for other keywords and other pages, but as soon as linking back from pages with pictures (and a small amount of text) is involved, I lose rankings.