Chrome: Nobody likes horizontal scrolling. Unless you have a mouse with two scroll wheels, there's no quick way to do it, or so we all thought until we discovered the Shift+Scroll shortcut.
While it's not a new feature, most of us need to scroll horizontally so rarely that we might never find it. However, if you hold down Shift while scrolling with your scroll wheel, the page will move left-to-right instead of up and down. Pretty handy for the two times in a year that you do need it!