Cool little Easter Eggs on websites are always greatly appreciated. Jokes aside, helpful error messages are very important for both usability and accessibility.
Filling out forms can be one of the most frustrating exercises on the Web, and making sure that users know and understand exactly what you are expecting from them, and allowing them to enter their information naturally and intuitively greatly helps ease that experience.
From an accessibility perspective, that which cannot be seen is as important as that which can. The presence and correct use of <label> tags can make a world of difference to the visually impaired.
Well, that’s cast rather a gloom over the evening, hasn’t it?
Always look on the bright side of life *whistles* :-)