In 1980, the median finishing time for male runners in United States marathons was 3 hours 32 minutes 17 seconds, a pace of about eight minutes per mile. In 2008, the median finishing time was 4:16, a pace of 9:46. For women, that time in 1980 was 4:03:39. Last year, it was 4:43:32.
http://www.nytimes.com/2009/10/23/sports/23marathon.html?_r=2&hpw