THE CONTROVERSY OVER THE EM DASH. This wikipedia article describes the em dash this way: “the en dash (–) and the em dash (—), named for the length of a typeface’s lower-case n and upper-case M respectively.” Its use is controversial, with prescriptivists concerned over excessive use of the em dash. This article in Slate by Noreen Malone was partly inspired by a blog post by an editor at the New York Times which scolded Times writers for overuse of the dash, including the use of five dashes in a 3.5 paragraph story. Noreen Malone tries to see how many em dashes she can work into her article, partly to demonstrate how excessive use can interfere with the flow of a sentence.
Noreen Malone cites Emily Dickinson as “Perhaps the most famous dash-user in history”. She quotes a summary in the Emily Dickinson Journal which gives the flavor of the low regard that some have for the dash: “Dickinson’s excessive use of dashes has been interpreted variously as the result of great stress and intense emotion, as the indication of a mental breakdown, and as a mere idiosyncratic, female habit.”