I sent my D600 to Nikon today. There are many spots on the sensor after 750 clicks, dust and larger circles that are probably oil drops.
I am perfectly capable of cleaning the sensor myself, and will do so in the future if needed. However, Nikon needs to feel some pain on this issue. So I will let them pay for at least this first cleaning - they understand the cost of warranty work, that will get their attention faster than signing a petition. All the better if they also replace parts to fix the problem permanently.