Over Christmas, Rap Genius was penalized by Google for unnatural links. In short, they offered an exchange of traffic for keyword rich links to their site. It was outed, Google's Matt Cutts saw it, it lead to a manual action that had a serious impact on their traffic.
Quantcast shows an increase in traffic to the site since the penalty was lifted on Saturday, will it go back to normal levels? Wait and see how the week goes. SearchMetrics doesn't show much of a traffic change yet but it may be too soon.
Would any other webmaster with such a penalty be able to get back so soon? Doubtful. :)
Rap Genius did lay it all out there and go through what led to the penalty, what they did wrong and the details, in very explicit terms. Plus, how they recovered, the steps they took, in detail. It is actually an excellent recovery post.
For more details on this story, see Techmeme.
Forum discussion at WebmasterWorld.