I have just found this in WMT
Pages from this site appear to contain spammy user-generated content. The problematic content may appear on forum pages, guestbook pages, or user profiles.
None of the said URLs exist. We have 4 million posts and work tirelessly to remove spam. No spam exists on our system for more than a couple of hours max, and that's only if the entire team is in bed. How badly could this manual action have effected us? Unfortunately it doesn't have a date on it so I cannot check against traffic.
On another note, the day Penguin hit, the website traffic went from 80k visitors a day to 40k. Not a single link was ever built to the website, not one and yet it has tons of awesome links from national/international press etc. I found around 1,000 very questionable links, negative SEO?
I actually manually emailed over 1,000 websites and did so 3 times over the course of about 3 months. Then I submitted a disavow file, which I resented doing with a passion. Despite exhaustive efforts to remove junk links, we have been unable to recover.
This website is the authority in the niche and so these idiot spammers, in the same way they link to Wikipedia, link to us. Our domain name is single word, 4 letters and the biggest keyword in the niche and they ALWAYS use this #*$! term when linking to us, because its our domain name. Now we don't rank for it. Despite a 10 year reign at number 1 and rightfully so.
Today I emailed Google, with a rather passionate plea but I am not hopeful. I am not sure what else I can do with this but it's driving me to distraction.