Terry Pratchett claims that a person's mental stability is inversely proportional to the number of exclamation marks they use in a document. An exclamation mark is a powerful literary device. It should not be added hither and thither all over your message, as this degrades its impact, and infers that the author does not know how to use them correctly. Either that, or the author is in a state of profound and hysterical excitement. In his own words : "Multiple exclamation marks are a sure sign of someone who wears their underwear on their head. " Multiple exclamation marks are used ironically in a number of web comics, notably Jerkcity, which uses them to parody the over-zealous and cynical marketing speak of the Disney Corporation among others (#424). They are also part of the lingua franca of AOL and IRC.

(Although I should mention that an otherwise well adjusted friend of mine is guilty of using them a lot.)