I have been working on a blog network for a few months now; it had over 800 pages indexed in Google. Around three weeks ago I tried out the DP Coop Network on these blogs and a week later all of the pages except for about ten were dropped from Google. I took the coop off and now the pages are just now coming back - I'm at around 600 pages in Google now. The only thing I did differently on these sites was add the coop, so I'm pretty sure that that's why they were dropped. I also tested the coop on another site that has been online longer and has some great backlinks - none of this site's pages were delisted - so I think if you have an established site - this may not hurt you AS badly as putting it on a new site.
Pretty obvious, if you place 10K links to a domain that is just few days old it will attract a lot of attention
Maybe not - I just thought I should share this experience, though. I started looking into it after so many pages of mine got dropped, and found that even Matt Cutts said it can be bad for your site (he specifically named the co-op): http://forums.digitalpoint.com/showthread.php?t=584694&highlight=matt+cutts+coop
Oops. The thread I had brought up was just mentioned above. Ignore this please. PS >> My personal experience? Yep, if they find it, you get nuked.
Everyone is completely ignoring the part about paid links...something Google has made very clear that they don't condone.