Aero Shake is one of several new Aero Desktop Enhancements in Windows 7, but unlike other such features--like Aero Peek and Aero Snaps--Aero Shake has never been broadly discussed in public by Microsoft, nor does it appear in their official Windows 7 Beta reviewers guide. That's right: Aero Shake is a secret. (Well, it was: Microsoft now admits to the feature.)
Aero Shake is as easy to describe as it is difficult to discover: Simply click and hold on the grabbable area of any floating (non-maximized) window and shake your hand left and right vigorously. (This works much better with a true, external mouse than it does with a trackpad, thumb nub, or other pointing device, in my experience.)
When you do so the first time, all other open windows are minimized. Repeat the action, and those minimized windows will be restored to their prior state.
Aero Shake is designed as an adjunct to Aero Peek, though it works a bit differently. In this case, the focus is on the selected window, as you'd expect. And other windows are truly minimized: That is, they disappear from the screen entirely and you don't see a "ghost window outline" as you do with Aero Peek.
Secret: Aero Shake first came to light in the wake of the October 2008 Professional Developers Conference (PDC), at which Microsoft unveiled most Windows 7 features to the public for the first time. Enterprising hacker--and Windows 7 Secrets co-author--Rafael Rivera of Within Windows fame discovered Aero Shake while unlocking Windows 7 build 6801 to include the new taskbar features that Microsoft had tried to hide.
Tip: Users of earlier version of Windows, including XP and Vista, can download a free utility that adds Aero Shake functionality to their desktops as well.
Tip: You can also trigger the Aero Shake effect--well, not the shaking bit--with the keyboard shortcut Windows Key + Home.
Here's a video showing Aero Shake in action.