Well, being that I worked in an Apple store, here's what I showed people. Sorry if I'm cheating here.
-The difference between where menus are (Apple has menubar, Windows has each app with its own menu.
-Spotlight
-iPhoto. I'm a photoshop guy, but iPhoto is simply amazing for lower end, not so technical folk.
-Expose
-Dock
-System Prefs (they can't believe everything is so clean and organized in there)
-How to set up your network in less than 5 minutes
-Automator. It's truly not that great, but there are some features in it that most people don't know about, that save tons of time. And its easier to use than most think).
-Debunk myths about viruses, multi-button mice, hardware compatibility.
All of that would take about 10-15 minutes with someone who's more inclined to technology. Others could take anywhere from 30 minutes to an hour.