People sometimes ask me why I do it, and I have never came up with a definitive answer. It consumes a large amount of the little free time I have, my legs always hurt like hell, and I will never ever come in first place (overall, I've won some age groups). Heck, I ran for 3 hours on Saturday in 20 degree weather with 30MPH winds and roads covered with ice. My wife gets upset when I leave her with the kids to go running.
And I love it. I think I'm going to run Chicago this year.