When I qualified for my first Boston marathon, and registered for the race, I ordered the official race jacket with the logo and all that.
I wore it a few days before the race to work, and someone commented on it at lunch that it hadn't taken place yet.
That year (2007) was nearly cancelled due to horrible weather, and I had one of my worst races ever, walking the last 6 miles after being on a 3:05 - 3:10 pace through the Newton hills after Wellsley.
Lesson learned. Don't count your chickens before they hatch!!