I've recently heard about android's isUserAGoat method and I didn't know what to think.
At first I laughed my brains out, than I was embarrassed for my lack of professionalism and tried to look into it and see if it makes any normal sense.
As it turns out it is a joke (as stated here) and it appears that other languages/apis have these sort of easter eggs implemented in their core. While I personally like them and feel they can be a fresh breath sometimes, I think that they also can be both frustrating and confusing (and you begin to ask yourself : "can users be goats?" or "I get it! "goat" is slang for.... wait..").

My question is are there any other examples of these kind of programming jokes and what are their intends?
Should they be considered harmless or not (how do programmers feel about it) ?
Do they reach their goal (if any other than to laugh) ?
Where do you draw a line between a good joke and a disaster? (what if the method was called isUserStupid?)