According to this post on dpreview, Nikon will have a new product launch in Dubai on September 13th, 2012:
I just got invited to a Nikon product launch event in Dubai on the 13th. They aren't telling me what they will be launching just the following:
"Nikon is delighted to invite you to a showcase event celebrating the launch of the latest additions to its DSLR range."
My initial information was also for a September 13th announcement. At that point I am convinced that the D600 will be introduced next week. The big question mark is still the price - if Nikon manages to keep it under $2000, I think the D600 will be a huge success (Sony's a99 24MP full frame camera will sell for $2,800) and will probably greatly surpass D800 in terms of sales and pre-orders waiting time.