In the past decade (2000-09), U.S. half-marathon finishers have grown from 482,000 to 1,113,000, a 131% increase. From 2008 to 2009, the number of half marathon finishers increased by 24%. Another interesting statistic- 57% of all half marathon finishers were women! -runningusa.org
I'm not surprised that the median time is slowly increasing, from 1:57:45 in 2002 to 2:00:21 in 2009 for men. The median finish time for women in 2009 was just under 2:20, or 10:40 per mile. I suspect a growing number of walkers entering races skew that time down considerably.
The half marathon distance makes perfect sense- challenging but still an achievable goal for most former couch potatoes.
In case you are wondering, the largest half marathon in the US is the OneAmerica 500 Festival Mini-Marathon in Indianapolis, with 30,281 finishers in 2009.
Interested in training for a half marathon? Check out Hal Higdon's Twelve Weeks to a 13.1 Mile Race.