As smartphones outsell feature phones, and tablet sales boom, mobile devices in the U.S. will become the preferred means of Internet access within four years. By comparison, the number of users going online via PCs "will first stagnate and then slowly decline," IDC said in a .

The mobile migration will begin in the U.S., with Western Europe and Japan soon to follow.

A boom in the number of global Internet users will transform the online world as well. IDC predicts 40 percent of the world's population, or 2.7 billion people, will have access to the Internet by 2015--up from 2 billion in 2010.

Advertisers, naturally, will follow the crowds. Worldwide online advertising will nearly double from $70 billion in 2010 to $138 billion in 2015, IDC forecasts.

So does this mean the is underway? Not exactly. With PC manufacturers of personal computers each year, it's still a stretch to say the PC is dying. It's not even sickly, in fact.