The feature now known as Aero Peek wasn't born that way. It went through several iterations before becoming what eventually shipped in Windows 7.
At the MIX09 conference, Stephan Hoefnagels showed some of the precursors to Aero Peek. Here are the highlights, and the corresponding time codes if you want to jump straight to the demos.
Thumbnails in the taskbar (time code 30:20)
How it worked: Instead of labeled icons, the taskbar showed miniatures of the windows themselves.
How it got its name: Um, it was just named after what it was.
Why it failed: When shrunk to taskbar size, most windows looked the same: white with unreadably tiny text.
Aladdin (time code 42:34)
How it worked: To bring another window into view temporarily, shake the mouse over that window. The longer you shake, the longer the window stays visible.
How it got its name: From the folk tale in which the hero summons a genie by rubbing a magic lamp.
Why it failed: It was too tiresome having to keep shaking the mouse while you read a document.
Bat Signal (time code 31:10)
How it worked: When you hover over a taskbar button, the screen darkens, and a spotlight shines on the corresponding window.
How it got its name: After the distress signal used in the Batman series.
Why it failed: People liked the way it helped them find their windows, but it was too easy to trigger accidentally. Also, people tried to "ride the light beam", which inadvertently canceled the bat signal.
Squeegee (time code 33:10)
How it worked: When you hover over the pop-up thumbnail, the corresponding window comes to the front, and all the other windows turn into glass sheets.
How it got its name: It makes your screen look like somebody took a squeegee to all the other windows and washed all the pixels off them, leaving clean sheets of glass.
Squeegee won the day, and it was given the official name Aero Peek.