I d like to share my experience with what i think is cross linking penalty between several domains on the same IP. I decided to cross link all my websites that are hosted on the same IP. They are all adult related so i thought there would be no penalty. Here are my evidences of the cross linking penalty presence. On the very same day, the google traffic for all the cross linked websites dropped by 50%. I think it is due to cross linking for several reasons: -It dropped on the very same day. -I checked all the incoming links prior to this day and i did not find an incoming domain that was shared by all the cross linked domains. Actually an incoming domain could be responsible but no one was on every incoming links list for each of my domain. -I checked the incoming domains prior to the day and none were banned by Google. (no N/A pagerank, no de-indexed domain). - One of the website did not receive any new incoming links except the links from my other domains during that time. I deleted the links from my "links scheme" 10 days ago, none of my websites recovered yet.