I have pressed it more than a few times lol, but I also use it alllllllllll the time. I just press it and type in whatever program i wanna open. Faster than clicking on an icon. A registry edit to disable bing search definitely made it way nicer too. Now no web results show up
Use i3-wm with linux and it's gonna be the only key you use :p
Also it is useful in Windows. I find myself using it in combination with D (minimize all windows) and L (lock the screen), or just by itself to search for apps.