I came across this Post Penguin 2.0 Spam Report form while going through Matt Cutts tweets:
Google Penguin Spam Report Doc
I appreciate the efforts put by Google to contact the webmasters and users. While there are few speculations that some people will abuse it by submitting the genuine sites. However, I believe there are always pros and cons attached. Google must have some process in place to deal with these abusers. In the mean time, feel free to report the spammy websites through Google Penguin Spam Report doc as mentioned in Matt Cutts tweet.
Happy Spam Reporting!