Globetrotter - 9:24 am on Sep 28, 2011 (gmt 0)
Over optimization might indeed be a cause of the problem. I thought about this aswel. I use the same backlinktext on the whole website to link back to the category page also with a lot of user generated content.
I tried to reduce the number of internal links but that was not a succes, maybe I should find a way to diversify the backlink text.