I wouldn't be surprised if you were the only MDA junkie. Marathoning isn't exactly encouraged. How do you plan on training for it without turning it into chronic cardio?
There is a half marathon coming up in the fall and I think I will run that one. No training, just show up and run it. I did two half marathons in 2007 and 2008 with training, so it'd be a hoot to see how well I do without.