Oh dear, that's three posts in a row with exclamation marks in their title! (And this makes four!!)
According to strict grammarians (and their blogging equivalents), "People tend to use a lot of exclamation marks in informal writing such as emails or text messages, but you should avoid using them in formal writing."
When did this controversial punctuation mark first come into English usage?
The exclamation mark was first introduced into English printing in the 15th century to show emphasis, and was called the "sign of admiration or exclamation" or the "note of admiration" until the mid-17th century; admiration referred to its Latin sense of wonderment.
...though the first point links (in the footnotes) to an obscure 19th Century American typewriting manual, and the second point links to
noted academic and historian Lynne Truss.
Googling around isn't helping settle the matter, as Mr Google seems to agree that no one's sure about the origins of the exclamation mark, though the best guess seems to be that it derives from Latin as, in Latin, the exclamation of joy was io, where the i was written above the o - and, as all of their letters were written as capitals, an I with an o below it looks much like an exclamation point.
We may have had Westward Ho! (Charles Kingsley novel (1855) leading to the naming of an Devonian town (c1865)) and Miss Haversham saying "play, play, play!" in Great Expectations, but what is the course of the exclamation mark from those early days through to their post 1970s' flowering (when they begin appearing on typewriters)?
Answers on a postcard!!!!