Jim Haley is correct about desktops eventually having an irrelvant marketshare but i feel as though he got the timeframe wrong. In places like offices and schools we will always have desktop computers for reasons like price, longer hardware lifespan, and being able to swap out a keyboard on the fly when someone spills something on theres. It's a safe bet that desktop computers will always have a home with certain people like me, the enthusiasts and hobbyists. I live in the real world though and so does everyone else. People buy according to there needs and wants. People dont need an anvil that is anchored to a specific room with no portability. They just want a lightweight no frills facebook machine to maybe browse some internets and type up a word document when need be. 
     This is there requirement for a computer and because of that they will almost always go with a laptop now a days. Quite frankly, it's something I cant hold against them but if someone chose to limit themselves to a tablet or smartphone I would find there choice a little obtuse.