Well, first we need to agree what the PC is. Let's say for the sake of argument that it's desktop and laptop computers. Then all other devices - ipad, phones, etc., are mobile devices.
Steve Jobs said something like this about a year ago:
Long time ago there were mostly trucks. But when population moved to more urban settings, there appeared a need for a car. Did the truck die? No, we still have them, but there are much fewer trucks now then in those early years.
So his take is that there will still be desktop computers but mostly for professional use. Your regular consumer will mostly use mobile devices. This transition may make many people uneasy.
Looks like the transition is making Jakob Nielsen a little uneasy. In his latest Alertbox (August 29) he writes that he disagrees with an opinion that "mobile devices will be the only important user interface platform in the so-called "post-PC future" (http://www.useit.com/alertbox/3-screens-transmedia.html).
He states that PC's have :
1. Much larger screens
2. Better input devices
3. Faster bandwidth
4. Hardware oomph
5. Software maturity
His conclusion: "use of mobile devices will dramatically increase, but much high-value use will remain on desktop PCs. Most companies must support both device classes, and our usability research shows that this must be done with separate UI designs that target the different characteristics of the two types of user experience. One size UI does not fit all screen sizes".
What do we think?