Frankly I enjoy Facebook far more through my iPad than I do through a desktop computer. That aside, the market for desktops is dismal, it hasn't gone anywhere in years. The GROWTH is in mobile devices. Yes, Microsoft's 90% of the desktop market will deliver a nice steady return year after year for at least a decade more. But nice steady return with a fade out possible in a couple decades is what is commonly called retirement and is presumably not the way to run a computer company.
Touch interfaces are here to stay, at least until direct neural input is possible. On the desktop we'll see traditional keyboards and trackpads/mice augmented by touch. Nobody wants to do database entry on a touch screen, but what about occasionally touching to get a photo in the right angle? Or on a browser? Or in iTunes?
Nowadays, people have multiple computing devices. Desktops, laptops, tablets and smartphones. Some people can live with just one of these, but a large number have more than one. I love my iPad, it's nice to kick back and surf the web on it. If I have serious work to do, there's always my MacPro and of course my iPhone for simple quick things there's my iPhone. Several times now I've found myself just sitting down to eat a restaurant and getting the call from work that one of my servers is having problems. It's usually a two minute fix, and I can easily do it with my iPhone. What I'm finding though is my MacBook (laptop) is starting to gather dust. I now pretty much only need it in hotels during overnight stays.