Stephen Wolfram, creator of Mathematica and Wolfram Alpha, has tracked life metrics since 1989, including daily outbound emails. The data are noisy, but averaged by month, works out to about 50 per day, with a mode (most frequent value) of 20-25. /Inbound/ email ranges about 300.

ReCode's Walt Mossberg reports about 350 emails/day.

The NYTimes comment moderation team handle 800 comments/day, each.

http://blog.stephenwolfram.com/2012/03/the-personal-analytics-of-my-life/
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@frankiesaxx That'd be interesting to get a real look at. I suspect we're exposed to far more causual writing now than in quite some time.

As of 1800, only about 25% of Europe's population was literate, and earlier than that rates may have been as low as 5% in rural areas. The culture of letter-writing itself had to be developed, and use of postal mail was a fairly newish tradition in the 19th century, for the general population. Books gave specific guidance on style.

@vfrmedia @frankiesaxx And before it was French, it was Latin.

Prior to the invention of the printing press, writing (and copying) books was hugely more expensive than reading. It was far easier to standardise on language, and train readers in that common language, than to produce books in each localised language.

In labour time, a book represented 1/3 - 1/2 a man-year of labour, for the scribe alone. Plus 300 calves for the vellum. About $0.5 - $1 million.

@frankiesaxx @vfrmedia The history of printing tech, costs, rate (impressions/hour), etc., is pretty fascinating.

In the 19th century, printing rates increased from about 180 impressions/hr. to > 1 million impressions/hr., per press.

Cast iron, steam, steel, electricity, rotary presses, webbed presses.