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It really is glass (another thread showed a pic of a cracked one) so I'd say you're safe.
 
Mine is "stained"

My 2.4 Al Macbook's trackpad does have a small stain or discoloration at the very top near the middle. It looks like it's below the top surface. It appears that the new trackpad consists of a thin layer of glass overtop the touch sensitive surface. It looks like the touch surface is discolored or stained. The spot is not any geometric shape, just random. I don't know if this is related, but I've noticed that if I run my finger left to right along the top edge where the spot is, it does not register the movement, the pointer stays still. I have to move my finger below the very top edge for it to register movement. The other three sides of the touchpad do not appear to do this. I thought about calling Apple, but maybe I'm being nit-picky. What is there policy for returns? I bought mine on Friday of launch week, so it's not quite 3 weeks old. Would Apple replace it without any fee?
 
If there is no coating on the glass then I doubt it could stain, but I dont know f thats the case.
 
I have to move my finger below the very top edge for it to register movement.

Same with mine. I doubt that it's a defect. I'm sure they felt no need to extend the sensor to the very edges. I do not have a stain however.
 
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