The Washington Post had an article about how half marathons are becoming so popular, especially among women. In fact, women are now in the majority in most half marathon races at 57%!!
Here's a dynamic graph that shows the popularity of the search term 'half marathon' (i.e. how many people searched for this term as a function of time)
Why are halfs so popular? As the article points out, running 13.1 miles is a significant achievement (doesn't hurt the word 'marathon' is in the name of the race) and the training doesn't take the amount of time that a full would require.
Notice the steep rise to the curve...you can also see a double peak for each year.....corresponding to the spring/fall race seasons (?).
This week I did 41 miles of faster running. Pushed myself a bit hard, but figured I could absorb the stress because of the easy 2 weeks on holiday.