I rather like Windows 8, but this new "feature" has been a source of substantial annoyance to me. It's badly thought out, because it is an unnatural consequence. When a user moves a window to the edge of the screen, it's probably because they want it there. Mostly, it's because they want to use another window. So to make the moved window full screen is perverse.
But at least there's a way to switch it off, for the sake of our sanity!