Never one to let an opportunity to explain a technology with a metaphor pass him by, Steve Jobs compared the transition from PCs to tablets as similar to when people stopped buying trucks and started buying cars (which is a dubious view of history, but let him run with it). From Engadget:
When we were an agrarian nation, all cars were trucks. But as people moved more towards urban centers, people started to get into cars. I think PCs are going to be like trucks. Less people will need them. And this is going to make some people uneasy.
I actually think Steve is both right and wrong about this. What’s more likely is that a lot more households will again become one-PC homes as the need to do intense writing, coding or other keyboard horsepower activities gets more evenly distributed as other kinds of applications migrate to tablets. Only time will tell, of course.