Having reached 100 million iPads shipped in 2.5 years the natural question is how long will it take for the next 100 million iPads?
The ramp of cumulative units shipped is shown below.
I also added the equivalent ramp for the iPhone. [The last data point for the iPad is based on an estimate of 16.5 million units in Q3 which may need revision depending on company reporting.]
The next 100 million will depend to a large degree on the success of the new iPad mini. To make an estimate we have to realize that there are several aspects of the tablet market which differ from the phone market and that therefore the predictive power for previous data is weak.