I'm seeing 3 sites, 1 my own, 2 by other people in my area, which have all tanked. The only thing i can see in common is that all 3 sites have their link text the same or close to the same for most of their links. These are really small sites...say 30-40pages 30-40links in been in the index for 3 years. I'm betting on a filter which is triggered if a percentage of your link text is identical downgrading the whole site. My site is still there..all pages still in the index...pr the same. ranking nowhere for unique company name. Only starting to rank in top 100 when searches are really specific say 500 results. Any site even mentioning my site is guaranteed to come above me.