The Multi-Window feature is a lot different than the QSlide used on the LG Optimus G, although the goal for both is the same. With QSlide, two apps are on the full screen at the same time, and one becomes more translucent and the other becomes more solid looking by using a virtual slider. The advantage with QSlide is that you don't have to cut the screen in half to use two apps at once, which could make the screen feel cramped.
For AT&T customers with the Samsung GALAXY Note II, starting tomorrow you won't have to be jealous of those who bought the phablet from another carrier. There still could be some envy from those with the stateside version of the Samsung Galaxy S III, who are supposed to get the Multi-Window feature with the next update to Android 4.1.2 from the Android 4.1.1 OS build that is currently running the device for all four major U.S. carriers.