Microsoft may would like to kill it off, but the fact is, the PC is here to stay. Businesses won't go for all of these portable devices & gadgets. Windows 7 is a fine desktop OS for this purpose.
And what about all of the other PC hobbyists? There is still a market for building high powered gaming PC's, those with massive quad, six & soon to be 8 core CPU's, along with those sets of 16, 24 & 32GB RAM kits. They're going nowhere, at least in the near future. And to consider, these tablets & smartphones can do a lot, but they can't be work horses. Many tasks will require the PC.
And what about those who has 3 monitors going at a time, all showing different tasks? Try that with a tablet, or even a mid range notebook. Try crunching numbers at folding@home with one. I have to agree that the portable devices are gaining momentum. But they have their limits. At night, at the workplace, when these tablets are in their docking stations or wherever, it's a PC that it's info is going to & receiving the new data through.
The desktop market may be slowing, but take a look around. The majority of homes has at least 1 desktop in it. One reason for the slowing of desktop sales is that PC's of today are better & lasts longer. They have more reliable parts in them than before. And more are highly customizable.