The speed of information travel, 1798 - 2009
Michael Stillwell pulled an interesting chart out of a book called A Farewell to Alms. It's a table of the speed of important news reaching London. For instance, in 1805 the news of the Battle of Trafalgar took 17 days to travel the 1100 miles to London; that's a speed of 2.7 mph. By 1891 when the Nobi earthquake occurred in Japan, it only took the news one day to travel 5916 miles, a speed of 246 mph.
Nowadays an email or a Twitter update can travel halfway around the world nearly instantaneously. The 2008 Sichaun earthquake occurred 5100 miles from London with the first Twitter update in English occurring about 7 minutes after the quake started. Assuming the message was read a minute later by someone in London, that's 38,250 mph. Had the Twitter updater been right at the epicenter and able to send a Twitter message 30 seconds after the quake started and was read a minute later in London, that's 204,000 mph. Five orders of magnitude improvement in 200 years...not too shabby.