The results of our MacBook discoloration poll are in; 20% of TUAW reader's MacBooks exhibit discoloration. It's hard to judge how accurate these results are, but if the real numbers are anywhere near these levels then Apple has a serious problem on its hands.
Fortunately, there are signs that Apple has taken notice: the creator of StainedBook.info recently managed to get Apple to agree to replace the plastic on the top of his MacBook's casing. That's a big step, but I'm sure many MacBook owners won't fancy calling up Applecare every two weeks after their replacement starts showing stains again. Clearly, a more permanent solution is required.