British author Terry Pratchett mentions exclamation marks, and their over-zealous use, in three of his books...

"'Multiple exclamation marks,' he went on, shaking his head, 'are a sure sign of a diseased mind.'"
-- in "Eric(Faust)"

"Five exclamation marks, the sure sign of an insane mind."
-- in "Reaper Man"

"'And all those exclamation marks, you notice? Five? A sure sign of someone who wears his underpants on his head.'"
-- in "Maskerade"

He also notes in an interview about the order in which he answers his mail that he:
"stir(s) it all up and in fact answer(s) in the order:

From kids
Ones written in green ink on mauve paper
Ones with more exclamation marks than sanity dictates"