I commented in my postings for the Santa Cruz half marathon and the San Francisco marathon at how popular half marathons seem to have become lately.
Google now lets you embed search analytics in your web pages...here's the time history of people searching for the term 'half marathon':
Every day now I swear I see twice as many people on the road when I'm running as I did two years ago.
I went for a bike ride a week ago Saturday and I counted every runner I saw (this was early in the morning at about 8am). I counted 18 people, more than half were women.