You may remember the Windows 7 marketing campaign where they kept accentuating the snap method of splitting your screen when using two different programs. By dragging a program to the left it would automatically reshape your window to take up the left half of your screen. Then you can do the same thing to another program on the right side. This way you can easily use both programs simultaneously. Writing a paper? Have Safari open on the left side and Microsoft Word on the right.
Microsoft calls this Windows Snapping. You can also drag a window to the top and it will maximize automatically. Now you can bring Windows Snapping to Mac!