According to VGChartz numbers, 360 is already at 25 million (congrats MS), and according to majority complains from user/retailer the fail rate for the machine is about 16%.
So having this we simple do some maths: (16*25)/100 = 4
4 Million 360 already RoD'd. (Just for curiosity, that is almost half of the portuguese population)
Any console ever had this fail rate?