Got a cinema display too!
I went in to the store this morning and told them about the mix up and they said they are sorry, insisted I keep the MBP and gave me a 30" cinema display for all the stress that I went through.....

Just kidding. But I did went in and told them and they let me keep it. As many of you said I should just shut up and pretend nothing happened. But I'm almost 90% sure that they are not going to take it back.
1) it's an opened box item and they need to send it back to clean it up = extra cost for them, before they can sale it as refurb which wouldn't make up the difference. It would be easier for them to write it off as a lost.

So if Apples 1st quarter earning dropped thats because of me. lol. Like my friend said, "steve jobs might not buy another turtleneck, who cares? he needs to try v-necks."

2) it's no way they can make me pay for the differences either, since it's not my fault.
Under these premises the logical conclusion is to inform them so this transaction will be legitimized so to eliminate future issues.
Also, think about it, if anyone of you turns out to be the unlucky one who got the downgraded MBP (online orders not shipped yet) then what are you going to do? I can imagine you would have a very difficult time to convince them that you got a low end model in a high end box. I wouldn't want that to happen to me either. But once I speak up then Apple will have the information in their system which would make it lot easier to sort the problem out.
Now that it's been all cleared I can sleep with a even bigger smile on ma face
And thank you all for your kind advice.

MBP 2.5GHz 250GB HD 512MB VRAM 2GB RAM :apple
acearchie. you can go get your money back now lol
Same thing happened to me but I bought a 2.5GHz with a 250GB HDD, 512Vram yet I got the basic model!
I really wish I could find the guy that got my model!