Benedict Evans on mobile leverage.

Personal:

First, they are not shared and they are personal. Of those 1.6-1.7 bn PCs, a little over half are consumer devices, and a large proportion of those are shared. The others are owned by companies, and at the very least they’re restricted in what you can do with them for personal uses, and many of them are actually single-purpose devices. So it’s helpful to think about somehow discounting that PC base to reflect actually personal personal computers – by half, or more. Just as there’s a ‘full-time equivalent’, what’s the ‘personal computer equivalent’? It’s not 1.6bn – it’s probably more like half that.

Literacy:

Finally, the step change in ease of use provided by the new generation of operating systems changes what it means for someone to have such a device. A very large proportion of PC users would describe themselves as ‘not computer literate’, or at best getting by following ‘recipes’ within a narrow set of tasks, but far fewer say they’re not phone literate or even smartphone literate (though a curve obviously remains). The usability of this new class of devices of itself multiplies the reach of the internet.

These are very good points on how different the PC and mobile markets are.