iOS devices are flying off the shelves, according the most recent Apple earnings call for the last quarter in 2012. To be specific, they are selling at 10 devices per second.
There were 47.8 million iPhones and 22.9 million iPads sold last quarter. That is the rate of 6 iPhones and 3 iPads per second. Over 75 million iOS devices were sold during the quarter, which is a new Apple record.