US law firm Lieff Cabraser Heimann & Bernstein is currently collecting Nikon D600 dust complaints for a potential class action lawsuit against Nikon. This is great for Nikon D600 owners but there's been reports of Nikon D600's being replaced with Nikon D610's. If it is indeed true, this lawsuit won't happen because Nikon is trying to rectify the situation by replacing the cameras.
*UPDATE*
The law firm Zimmerman & Reed PLLP, filed a class action lawsuit in California federal court on February 19, 2014.