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I don't know if he was harsh, every site can be improved, it's the nature of the changing beast.

Large chunks of the content appearing on other sites is a big problem and could explain drop if Google has recently crawled/valued those sites.

I had already checked your KW density for "facebook login" and it is reasonable (not over the top).  That page is in the index so whatever your XML sitemap problem is, at least it is not keeping the page from the index.  If all other pages on your domain are okay and the XML sitemap problem was not related only to this page (which I am assuming), then that is obviously not the culprit.

If you're content is going to be syndicated/"borrowed", you might want to add the rel="author" etc. info to your site.

Q: Do you see any of the other websites' pages (with the copied content) ranking for your term?

Q: You didn't answer about link tracking.  Here's what I am getting out here..

Hypothetical: let's suppose a few weeks ago you have 40 external links to that page.  Let's say of that 40, Google may value 12.  Of those 12, perhaps 2 have great authority, relevance, PR, etc. according to Google.  And then, for reasons unknown, those two sites have removed the links to your page.

So if you have before/after tracking of inbound links, you might see a changes that wave a red flag.  It's just one more thing to check.

Joshua, I mention html validation and Ryan makes some points on ways to improve the site, but I'm looking for causation for the drastic drop in rankings for that phrase and that is what my previous questions are about.

While we wait for your answers, I will assume for a minute that you are absolutely positive that no changes were made to that page or the site recently and your inbound links remain constant, external site referrals and other analytics/log data do not indicate any problems.

Which essentially leaves you with link devaluation (algo change) or being dropped from the index for a bit.  Unfortunately your only course of action would be trying to improve site SEO and building & improving external indicators to help you get back up in the rankings for that phrase.  If that page was crawled and had errors or was not found and dropped from the index, time should help your cause.

Thanks.  I don't see any major issues with the page (although you have some html validation errors which should be tidied up).

Any changes made to that page/the site/.htaccess/robots.txt recently?

Do you monitor site down time, and if so, was there any corresponding down time during that period?

Did you track inbound links to the site before/after this happened?  If so, any big changes?

So, without any URL or KW example, usual suspects (answers) include: panda, junk link devaluation, or your page may have had tech problems and disappeared out of the index for a bit.

First two are self-explanatory.  One example of the latter situation, a domain name or hosting account that is let to expire, is crawled by bots after it expires (and they find the generic registrar/host page page) and BAM! that top 3 ranking nationally for a valuable phrase is toast.  I saw this happen with a client site that was down for less than 48 hours.  So they went from #3 to 70ish.  They are still trying to recover rankings and that was about three weeks ago.

So I would look real hard at your analytics and logs, particularly crawl logs and see if there are any anomalies.