Read the whole thing first.
Matt Cutts, the lead of the search spam team, posted in a Hacker News thread that is probably doesn't make sense to sue Google over negative results.
He is responding to post named Panda loss as libel where someone considered starting a company to just sue over negative search results. Here is the tweet with the idea:
Continued at: http://www.seroundtable.com/google-s...seo-15294.html
A link to Matt Cutt's post: http://news.ycombinator.com/item?id=4100159
If you can find more information to provide in this thread, please post the links.