Rob DeCastella always did a 30 mile training run about a month before his major marathons. He said it gave him confidence about being able to complete the distance and gave him strength. I'm thinking about doing this but I've read other sources that say anything over about 23 is counterproductive because you're depleted at that point anyway. Also read that KK does not do anything over 20k in the month prior to the marathon so as to have fresh legs on the day. What is the longest run you people out there do in preparation for a marathon and when do you do it?