Nice, my wife and I want to do the Goofy Challenge one of these years; Disney was her first marathon. Richmond was one race I was looking at this fall, but I chose Philadelphia instead.
The one thing that really caused me to start training seriously was the realization that I had potential to be a better-than-average runner. As I mentioned, I was profoundly mediocre in high school and for the first two years of college. Then I transferred to a 4-year school that had a pretty good cross country/track team, and I dropped a minute off my 5K time in just a month of training with them. Each year since then, I have steadily improved, and each improvement brings me new motivation to see what I can do.
Just as an example, when I transferred to that school, my 5K PR was 19:30. I ran 18:25 after one month, and then 17:24 the next year. After that, I made it my goal to break 17:00. It took me several years, and during that time, I wasn't even sure if it was possible for me to run that fast. I mean, sub-17? That's crazy fast! This past spring, I came within half a second of breaking 16 minutes, but it's taken me 4 years to drop that last minute.