martinibuster - 11:12 pm on Aug 20, 2008 (gmt 0)

Longevity is not a measure of how clean a site is. A site can rank well for many years on a poor foundation.

How original is the content?
Of sites I've inspected that have ranked well for years then were suddenly slammed, a fair amount have had content originality issues. Mostly this involved aggregation of content from various sources, like YouTube, Wikipedia, iMDB, etc.

Links, buying, selling, acquiring from partners
This is always a sensitive issue. How were the links acquired? You say there's no interlinking, and that's good. That the sites are related in theme may be less good. It certainly makes it difficult to acquire unique inbounds for each of the related sites so as to not have their link relationships overlap.

I'm not saying you engage in risky link schemes, just pointing out a common pitfall. A common webmaster quirk is the inability to see the difference between optimization and well, spamming. So a webmaster who really wants to get to the bottom of what's going on, has to be brutally honest with themself of about edgy link building and content issues. No making excuses like pointing at others who do the same and are still ranking.

Is it possible this is a hand check or is it algorithmic? Could the June thing have been the point where your network came under scrutiny?