bbarbeau - 2:41 pm on Sep 2, 2010 (gmt 0)
olly, how has this shaken out for you in the weeks and months since?
I have a client who launched a redesign almost a month ago, and we've been experiencing very similar repercussions, so I am extremely interested to hear whether your site recovered and if so, how long it took.
There were some differences between our situations, which I'll outline for the sake of adding to general knowledge. (Hope that isn't against forum etiquette; I know in the official Google forums it's a no-no.)
Anyhow, the client launched the redesign and within a few days slipped from page 1 to page 2 to nowhere for some of their most competitive keywords.
URLs remained the same, content (simply in terms of body text, product descriptions, etc.) remained largely the same.
A major thing I noticed in investigating the crash was that internal link size more than doubled in the wake of the redesign. Part of the jump was caused by going from a static, image-only top navigation section to a CSS-driven text link top nav with primary links going across the top, groups of secondary links dropping down on hover, and even tertiary links popping to the side when hovering over secondary links.
Moreover, the structure of these links in the source code was all jacked up... they displayed fine in the browser, but they read in the source going from right to left, and from secondary to primary (rather than primary to secondary and from left to right). This meant that all the mission-critical text links in the primary navigation were placed at the bottom of the navigation div in the source code.
Another issue was that the bulk of the body copy was relegated to the bottom 1/4 of the page. So we had them change around the order of the source, and removed the tertiary links altogether from the top nav. We've also recommended nofollowing many of the additional links, which arose from adding social sharing buttons, but they haven't implemented this yet. (There are no social sharing buttons on the home page anyways, which is the primary page effected by losses.)
So much for Google's advice of doing things for the end user, as if search engines weren't there. The tertiary links were completely meant to minimize the number of user clicks to get to their page of interest. But I think the result to Google was that they hemorrhaged PageRank throughout the site. (The site has enjoyed very nice boosts in Yahoo and Bing following the redesign.)
They still have internal pages ranking well for a few terms. But the home page is almost entirely out of sight.
site: searches don't list it as the first result. On a site: search, the home page ranks #221.
Unique text on the home page doesn't rank when searched for. Only a few scrape/spam sites do. (Exact phrase searches of interior page text does return the target page at #1.)
So yeah... any additional info about how your site has fared in the wake of the index page drop would help me out bunches I'm sure.