I'm mixed in marathons, on the one hand I don't see the point of it what situation would you ever need to run 26.2 miles. On the other hand I would like to do one it must be some feeling of achievement.
I'm up to 7 miles on a long run at the minute and want to push onto 10 but I'm not sure my knees will take it, if I do get to 10 then I'll push to 13.1 but it's a big if.