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I agree with EGOL's suggestion to have an expert look at the situation. We really don't have enough information here to be able to tell you for sure what has happened to your site, and what the best course of action is.

It's been a month or so since this was posted. Do you have any updates? Have your rankings changed? Did you figure out what might have happened? Anything for us to learn from or clues to try to help you more would be great.

the keyword isnt as competitive as "books". it's more in a niche market. however, some sites have the keyword in the url and most of the links have the exact anchor text. we on the other hand tried not to use the keyword in the anchortext as often... we are mostly linked like "brand + forum". I guess we need more links with the "keyword forum" and maybe onpage optimize. Thanks for your replies.

But still it's kinda confusing if Google sees keywords like "digg", "share" etc. as more significant as the actual topic ("coffee"). Also vBulletin is a well known forum software. I checked the vBSEO settings again and here is everything fine as well.