Nikon Issues a Service Advisory on the D600Users of the D600 have complained about issues with dust on the sensor and Nikon has now officially acknowledged that there's a problem. They say that since removal may be difficult with traditional cleaning methods, you'll be able to send the camera into Nikon for service.
"It has come to our attention that, in some rare cases, they may be reflected noticeably in images and removal may be difficult using normal measures," says Nikon in its official advisory. The company also says that it's important that owners clean their sensors regularly, and that standard maintenance should help to reduce the effects of this accumulation.
Nikon Service Advisory