Good take on iPad sales by Christopher Mims:

The mathematics here aren’t complicated: If iPads last a long time, and Apple is still selling a respectable 15 million to 20 million per quarter, most of them to people who have never owned one in the first place, the rate at which Apple sells iPads can stall even as iPads continue to take over the world—or at least the US and other rich markets.

I also like his argument for a tablet specific OS. With OS X being for PCs and iOS being for phones — the iPad would likely do better with its own variant of iOS/OS X that has been designed just for its larger screen size.