One of the minor, more handy features of Windows 7 is a new way to resize windows by just dragging them to the edge of the screen in a gesture-based action.
If you drag your window to the top of the screen, it will maximize and fill the space completely. If you drag it to the left or right edge, it will dock it to that side and take up roughly 60% of the horizontal space (notice the silhouettes of the larger windows). Drag it back down or over in the other direction and it returns to its previous size.
It's especially helpful when you're working on computers with small screens and trackpads, where it can be a hassle to get your cursor over that tiny button to maximise or restore to normal size. Instead of a small space to aim for, you at least have the whole upper bar to work with.