For 98% they don't understand any of it, because the extent of their computer knowledge is turning it on and off, surfing the net and getting their email, so demonstrating it is a total waste of time.
For the remaining 1%, I usually demonstrate a game by playing something like Crysis, after all their Ooohs and Aaahs, I offer them a chance to play themselves, but they are intimidated by my game play, and refuse to play, thinking they'll embarrass themselves.
Then there's the last 1%, that are drooling at the opportunity to play while I'm playing, and worst case is having to wipe the drool and spit off the keyboard, mouse, and monitor, when they finish.
That last 1% usually turn out to be dedicated Xbox or PS3 fanatics that leave wanting to know what it would take for them to have a setup like they just played on, and quickly get discouraged when they find out that one graphics card cost more than their entire setup.
"Lone wolf, calling Wolf den, over"
You're on your own Rambo, just live with it.