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Which full-screen application are you talking about? I guess you use Lion (from another thread), but your signature still mentions 10.6, thus the confusion.



Exit full-screen view
To bring an app back to the desktop, move the pointer to the top of the screen to reveal the menu bar and click the “exit full-screen” button on the far right.
from Full-Screen Apps
 
That's referring to my MBP.

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I did figure out that pressing Esc will do the trick.
 
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