Not everyone works in an office
I have 40 users working at 15 shared machines switching from a terminal emulator, running a LIMS, to various specialised laboratory applications running in the browser (IE8 on Win XP) to software interfacing with analysers (some of which hasn't been updated by the manufacturer since Windows 95). Oh and we're a Microbiology lab, no touching the screen (keyboards are a necessary evil that are cheap enough to be replaced). And we're only one of the labs here, and we're not a particularly big one.
Voice and touch tiles just won't do the job in this environment, neither will obscure methods of switching applications. And hiding running apps away is definitely out of the question, what happens then is people fire up more instances until the processor runs out of grunt and the system fan is whining like concorde.
I'll get my coat, it's the Howie one with gram stain down the front.