The number 42 is thought to be a reference to the movie The Hitchhiker's Guide to the Galaxy and in particular, the 'answer to the ultimate question of life, the universe and everything' (which of course is 42).
More interesting however, is the '42 puzzle' which is of significance here because this puzzle is solved by, among other things, using binary code and roman numerals, which could possibly relate to other secrets (Donkey Business and Fantastic!) within this site.
It is hypothosised that this easter egg, specifically the 42 puzzle, is the key to a number of other secrets, in much the same way that the secret on Where's the Sky? is the key to solving the interstellar envelope. If you look at the solutions to the 42 puzzle, you will see the earth, which is the 42nd ball from the start which may be a reference to the map on Diabolic, and the binary code used to decipher the 42 puzzle (Decimal), can be used to convert the decimal values on Donkey Business.