phones and tablets are fine for consuming media. they are noticeably worse at creating it.

i couldn't imagine typing out long responses, sometimes with links, with a phone or tablet.

as for how many consumers still use PCs, hard to say. i know i don't go a single day without using mine. whether it's to play a game, type up a guide for someone to do something, or whatever else. on the flip of that, i also own a ultrabook that i use when i'm away from home. it's capable of doing many things, but it's no where near as capable as my desktop setup.