This purchase is equivalent to stealing. The Apple store pricing was obviously in error. Apple took the ethical high road and sent you the macbook for $109 which shows that they honor their commitments. Apple did not have to send you the unit.
I hope you take a moment to think about this transaction. Imagine that YOU own a business that sells widgets in a window with a price marked $1000 on a sign. One day a zero falls off the sign and the price shows $100. Someone walks in off the street and asks for the the $100 widget. Do you sell it to the person? What if they ask for 10 widgets at the $100 price? Do you explain that there was an error on the sign? If you did sell the person a $1000 widget for $100, how would you treat that person when they come back into the store? Your store would lose money if you sold the widget for $100.
Yes, you did get a deal on the Macbook. Apple did honor the deal even though we all know that the pricing was clearly in error. The only person who doesn't have any honor or ethics in this transaction is the buyer!
I know you are happy you got a good deal and beat THE MAN. I hope you see that your ethics are wrong. The ethical thing for you to do would be to call Apple and talk to them about this transaction.
TFR
P.S. Rather than call Apple and ask for an exchange on the RAM in your $109 Macbook, I hope you take your 2 x 512MB RAM modules and shove them up your nose!