What are people's thoughts on ridiculously tough level bosses?

Personally, I find that they tend to kill the flow of a game (and the narrative too -- if there is a narrative).

I'm thinking that after the 30th time a person tries to defeat a level boss, the game should just give them the option to skip it (with some kind of penalty, be it a lack of bonus points or not receiving the associated achievement).

Some of us just want to get on with the game.