Everybody saw I was the first to post about the penalty I received from Google for using the Co-Op when many of us started seeing it happen to our sites. This was on June 21st 2006. It looks like it took about 3 months for the penalty to subside because as of this week (of September 21st 2006) I am finally showing up back on page one for SERPs where I belong. When I first realized I was penalized I removed the Co-Op and of course I will never use anything like it again. I didn't even need to use it and that was my biggest mistake. I too made sitemaps and attempted to contact Google with re-inclusion requests etc. I also tried using alternate pre-existent domains that I had. I also have since removed my sitemaps just this past week. I hope the rest of you see some reprieve as well. I should also point out that there are other websites that I have that suffered the same penalty and still have yet to see a reprieve. I will make another post if I see those clear up as well.
the co-op is just what it sounds like, a cooperative advertising network. more info is available here: http://www.digitalpoint.com/tools/ad-network/history.html http://www.digitalpoint.com/tools/ad-network/faq.html also, I've never been banned nor penalized for using the co-op network and I use it fairly extensively.
Two of my other websites have had the penalty lifted it seems. I have one more that hasn't been reprieved. Submitting a re-inclusion request might have helped because I did it for all but the one that is still being penalized.
It's a great way to get free links on other peoples sites. A great way to find people that might not normally find your site. But as with anything Google related, you are taking your chances.
I'm just getting into all this IM stuff but I know Google doesn't like schemes that produce Phony traffic to their paying advertisers web sites. I read anyone caught in a clickad scheme will be banned from using Google adsense. Maybe these co-op groups are considered to be Phony traffic shemes by Google. I still have alot to learn about what's going on. Thanks everyone!