OK, let me explain this clearly for everyone. No magic eraser or such other product will work on these discolorations. Many people have suggested it so far and suggesting it again will not change the fact that the majority of the people are not having success with it.
I would like to refer everyone to a very important website:
http://stainedbook.info
I came across it. If your MacBook was made in the 19, 20, 21, or 22 week, you may likely have this problem. It seems that this is the trend. I highly suggest you call AppleCare and even refer them to this webpage. If you yourself have th discoleration, then contact the webpage and contribute to the cause.
This certain batch seems to have a defect. That is the reason why there is discoleration. Not becuase people smoke, not becuase they are dirty people, and no amount of abrasive material will properly get it off. I use properly, beucase you can damage the plastic and still get off the stains (from what other have been reporting).
I want to asure everyone that though there has been a lot of talk about the discoloration, in comparision to the number sold, only a percentage have had defects such as these. There have been many other people who (like myself) have not experianced this problem.