Whenever this topic comes up I'm amused by the narrow perspectives that often emerge largely because posters often assume their requirements are representative of the much larger universe of computer users. It's certainly true that the iPad (or devices like the Kindle Fire) can be adequate replacements for many computer users, especially those who, before the iPad came along, were forced to "overbuy" laptops or even desktop systems to do little more than handle email, surf the web, and watch videos. For those folks an iPad or an even more portable device is perfectly adequate. And it's equally true that the iPad can't replace more powerful systems for folks like me who sit in front of five monitors linked to three separate cpus. But I'm not a typical computer user and I wouldn't denigrate the iPad because it fails to meet my overall computing requirements. I'm a member of a small minority of computer users.
On the other hand, there are millions upon millions of computer users for whom an iPad may be a delightful leisure time device but not an adequate replacement for the systems they use eight or more hours every day. I'm not referring to software designers, engineers, or financial analysts. I'm talking about the sort of folks for whom I design software -- office workers who don't wander about computer in hand from one meeting to another, who would find a ten inch screen that displays a single window at a time to be a productivity nightmare. Such folks don't need or want touch screens; they want to control their software from their keyboards or with a mouse. They want more screen real estate with access to more windows, not more portability.
As extrordinary as the sales of the iPad have been, laptop and desktop systems still constitute about 80% of all computer sales. Desktop sales may shrink but it won't be because most workers need portability; it will be because smaller cpu units can be more easily squeezed into small (and shrinking) cubicles and make more room for larger monitors with multiple resizable windows driven by more powerful chips. This Dilbert world may not be the brave new world that those who expect to spend their time jet setting from meeting to meetng around the world hope to see but it's the world that most white collar workers experience on a daily basis. And that world ain't disappearing.