I think a key indicator of the equilibrium point is the market share of mobile to desktop in emerging markets. I think we're going to see usage patterns in the US trend to those over time. For example, check out this graph from the KPCB 2012 internet trends report on internet usage in India: https://dl.dropbox.com/u/120/Screenshots/emerging_market_int...

The evidence in the US and UK seems to suggest that people that can afford desktops or laptops aren't so eager to abandon them. It seems just as likely to me that people in developing economies will upgrade to real machines given the chance.

It is actually different for economies like India. Majority of the population never had computers or internet. But everyone is starting to have a mobile phone.

They are doing an Ice -> Vapour thing skipping a step.

The graph you've linked to looks too symmetrical to be realistic.

If there are only two options that add up to 100% it must be perfectly symmetric.

But why do they add up to 100? What are they measuring to get the data -- traffic in the provider's networks?

Because that is how percentages work.

Comparing pure visits or pageviews to sites with a counter is not capturing the whole story. App interactions are not necessarily hits for a stat counter. A better indicator is time actually spent on different devices (which is not the same as 'time on site' in analytics). How many hours are people in front of a desktop computer and how much time do they spent on mobiles and tablets?

If you start on December 2008 and end in May 2012, it is much easier to see the trend. I agree that it is an exaggeration to say rapid, but it does look like a definite downward trend for desktop and upward for mobile.