Stuart Jeffries bangs away in the Guardian:
Novelists (at least male ones) are apt to be mean-spirited about dog's cocks. "Cut out all those exclamation marks," wrote F Scott Fitzgerald. "An exclamation mark is like laughing at your own jokes." It isn't actually. When one German starts a letter to another with "Liebe Franz!" they are merely obeying cultural norms, not laughing at their own jokes. Nor is chess notation, which teems with exclamation marks, especially funny. No matter. Elmore Leonard wrote of exclamation marks: "You are allowed no more than two or three per 100,000 words of prose." Which means, on average, an exclamation mark every book and a half. In the ninth book of Terry Pratchett's Discworld series, Eric, one of the characters insists that "Multiple exclamation marks are a sure sign of a diseased mind." In Maskerade, the 18th in the series, another character remarks: "And all those exclamation marks, you notice? Five? A sure sign of someone who wears his underpants on his head."
Amazing(!)