I would say the era of the typical user is over, not the PC.
What will change is a segmentation of the majority of users who consume their 180 characters of content, and users who actually use technology to create. In other words, those of us who develop technology will have to consider different kinds of users in a wider context (if we don’t already).
CAD for example is increasingly relevant and becoming even more resource-hungry. Content creators for that space aren’t going to move away from desktops.
I defy the average consumer to model their kitchen (realistically & with some precision, not blocks in Sketchup) on a tablet. Now, if we have a greater merging of more input devices with tablets, then we may see something more interesting.
I still think that tablets are often too small, and until the current crop of technologists & designers are retired with arthritis & myopia, they won’t appreciate how challenging tiny buttons and tiny (relatively speaking) screens can be.