How fast is the desktop PC giving way to laptops, tablets and smartphones?

Articles touting the imminent demise of the desktop PC abound. PC sales have indeed been decreasing, while laptop sales and especially tablet and smartphone sales are increasing. The PC is vital for many tasks performed in the corporate world and industry, whereas it might be no longer vital for recreational use. Do you think that laptops and tablets are bought as replacements for PCs - or are businesses and consumers buying them as supplements?

My observation has been that laptops and tablets are supplementary purchases while the desktop PC remains by and large firmly installed at the office or industry floor, but you might have examples where small, medium or even large businesses succeeded to oust the PC in substantial quantities, replacing them with tablets?

Have, for example, some of you replaced their NAS, their gaming PC, their self-built PC with a tablet, or are intending to do so in the near future?