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The largest site has about 300 pages and the smallest about 60. The content is all different (no duplicate issues) The one thing they have in common is we link to the most relevant sites on the Internet for the content.
There can be 10 or more out-bound links on a page. None of those links are sold and none of them are linking to badlands. In some cases the pages do look like directories.
In September, they started dropping in rank until they disappeared completely - meaning site:example.com returns nothing.
By contrast, we have a single site about < another topic >, done the same way with the same amount of out-bound links that continues to do extremely well.
If you put them side by side the only difference is, the sites that have been removed are about < a high interest topic > and the one that remains is about < a much less popular topic >.
The other thing they all have in common is a large amount of out-bound links.
[edited by: tedster at 2:36 pm (utc) on Sep. 20, 2008]
The pages that look like directory or link exchanges may have fallen into trouble becuase Google has been trying not to send users to pages that are essentially outbound links. I'd try getting more unique content into those pages and see what happens from that - maybe even remove a few outbounds from those pages at the same time so the balance shifts noticeably.