I just read a story under this provocative title, about one of the original creators of the IBM PC, now working for IBM Africa, who uses a tablet himself and thinks the PC is obsolete. If you want to know what the vox populi thinks, read the comments. They're not ready to give up PC's.
I think I'd say that you need to have the right tools for the job. If your job is sitting at a desk and creating content (text, spreadsheets, presentations, software, etc.), you're probably going to continue to be happiest with a desktop and a keyboard.
If you mainly spend time in meetings and on the road it will depend on whether you also create content. Tablets for those who don't; laptops for those who do.
It is fair to assume that in the emerging markets, customers may make different choices. It all depends on where you're coming from. If you live and work in the North American business environment, you are accustomed to working with a generous screen and a keyboard regardless of whether that means a fixed desktop, a laptop, or a laptop extended by desktop facilities (a larger screen, a better keyboard, attachment to peripherals). In countries which started adopting technology much later desktops are not so much of a phenomenon. Users started with laptops, netbooks, or smartphones. Tablets may represent much more power than what they are using now, not less as they do to current desktop users.
The PC is not dead, it is merely continuing to change. Whether I use a desktop, a laptop, a netbook, a tablet or a smartphone -- or something new we haven't imagined yet -- I am still taking advantage of what we learned by designing and selling PC's. In some cases, these are literally extensions of PC's -- in running the same operating systems or the same applications. In other cases, we are moving to operating systems and applications that take better advantage of new technology -- and fully acknowledge that unlike the age of the PC where keeping as much as you could on its local drive was very important, in the age of the cloud, you may need to keep very little local at all.
It's also good to remember that for anything as ubiquitously installed as the PC, we could agree to stop manufacturing and selling them tomorrow and it would still take decades for all of them to disappear.
The PC has made enormous changes in how we view data and computing; new devices and services will continue to do that. As we move frward with device choices to take advantage of new technology we will be figuring out how to use them in a world in which PCs will continue to play an important role for many years.