BeeDeeDubbleU - 8:52 am on May 24, 2012 (gmt 0)
E.g all links point to a particular page using the same anchor text.
I have two sites that were badly hit and I am as certain as I can be that it was caused by overuse of keywords in internal links.
One site lost more than 80% of its traffic. The other about 50%. On this one I weeded out a lot of the links and (with a slight upturn in traffic) there are signs that it will recover as a result.