Positive 1: Exposé + Dashboard

The first thing to show in OS X to your curious Windows friends is what you can do with just four keys of your keyboard. F9 to F12. This _is_ the most addictive feature of OS X. Once accustomed to it, you will miss them all the time in other OSs, unless they have something similar. Well, Windows has full analogue for F11, which is Windows+D, showing a desktop (you can think of it as instant minimizing all the windows). But on Mac, you press F11 again and all your windows are where you left them. And other two keys dedicated to Exposé go even further.

Press F9 and all your open windows will be tiled on the screen. The more windows you have open, the smaller tiles will be, but main thing is that all applications get displayed on one screen at once, with nice transition effect. You point your mouse over the application you want to switch to and click. You can do it without your mouse too, Tab key will go cycles through all applications. This is a bit better way to browse open applications than good old Command+Tab (Alt-Tab in Windows), because you are not just choosing application icon (which are much more beautiful on Mac, in their glorious size at least!), but see how this window looks like.

F10 does the same thing that F9 does, but only for open windows of current application. This comes handy if you have several Web browser windows open and want to jump to another window of the same application, which is not possible using Command+Tab.

And F12 is not Exposé, but its Exposé-like über-convenient togglable nature makes it very addictive. It switches on/off your Dashboard - set of applets, called Widget in Mac OS X. All that small applications you don't want to get listed in Command-Tab, and which you usually want to come up instantly, like Calculator or Calendar. You decide which Widgets you need and arrange them on screen by your liking. Konfabulator (now Yahoo widgets) looks great on Windows, but it is not that dead-simple and comfortable, and Google Desktop is a bit different and slightly less productive. Already because speed of using F9 to F12 keys is simply unbeatable.