From Eats, Shoots & Leaves by Lynne Truss:
Everyone knows the exclamation mark – or exclamation point as it is known in America. It comes at the end of a sentence, is unignorable and hopelessly heavy-handed. Here's one! In humorous writing, the exclamation mark is the equivalent of canned laughter.
Introduced by humanist printers in the 15 th century, it was known as "the note of admiration" until the mid 17 th century. Ever since it came along, grammarians have warned us to be wary of the exclamation mark, mainly because, even when we muffle it with brackets (!) it still shouts, flashes like neon, and jumps up and down.
Traditionally it is used:
in involuntary ejaculations: "Phew!"
to salute: "Jack!"
to exclaim: "You are so cool!"
to emphasize: "I mean it!"
