Easter eggs can be fun, but you got to be careful too! I know of a group that put a "PC Load Letter" error on a $100k machine as a joke (Office Space reference), all in good fun. Well years later a unit completely broke, kept saying "PC Load Letter", and caused a big problem for the customer. Somehow an executive caught wind of the whole situation and was not too pleased...

So maybe the moral of the story is put Easter Eggs where a user can find them to have fun, not as an error message!