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This is actually a reasonable question.

They changed the way that waking a macbook from display sleep worked. You used to be able to just swipe the trackpad to wake the screen back up and now you have to click a key. This occurred in the SL > Lion transition.

Not a huge difference but I did prefer the old way.
 
My MBA wakes up when I open the lid. If the lid is open I I just click on the trackpad and it wakes up. Never tried just swiping.
 
I alway use the down arrow button to wake... I have this concern that if I click the mouse I'll be clicking on the OK button to either empty my bank account or erase the had drive 🙂
 
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