One of my sites (PR6) has been at position 2 in a search that returns a total of 38 million results for around 10 months and in the top 10 for about 2 years. The site is 6 years old.
At the end of August it dropped to page 5, yoyo-ing between page 5 and page 4. No other sites were affected that were around it.
I made no changes to the site prior to the drop, nor did I add any outgoing links or, to the best of my knowledge, aquire any significant inbound links.
When I perform a Related search on this domain, it comes out at the end of the list. In fact all of my sites suffer the same problem with the exception of one, which is only one that doesn't link to a directory I run for my market sector. Yeah - I suppose really it's just a glorified link farm.
This site and all of the others have retained their PR, and any other sites that link to the farm come out in the number one position for a related search on their domain.
I've kind of reached the point where I'm wondering if I should abandon the site and just move on to the next project rather than keep tweaking it in the vague hope of restoring it to something approaching its former position in Google.
So on the evidence of my own sites I'd say the problem was related to the farm, but looking at other sites linking to it I'd say not, unless of course my sites are being targetted through the IP addresses.
I've deleted a vast amount of duplicate content from this site over the past 2 weeks in an effort to eliminate the penalty (if that's what this is).
Any idea what would cause a site to appear last in a related search on its own domain name, or is this not uncommon?