Marathons are first-person phenomena, hard to write well about. But there are exceptions, good online journals that occasionally feature their authors' distance running experiences. Some at the top of my current reading list, full of humor plus fine prose:

• http://sprintbare.com/run — Brian Tresp (and friends, several Washington DC area runners; of the current participants, I'm about half as fast as everybody else) ... Brian is a Macintosh enthusiast, a fan of the movie Fight Club ...
• http://www.anstyn.com — Adam Safir — local (DC area) runner ... superb commentary on a wide range of issues ...

TopicRunning - TopicJournalizing - TopicWriting - 2004-02-08

Inactive (or less-active, currently):

• http://runnersblog.blogspot.com/ — Sean Lloyd — DC/Virginia area, self-described "beginner" ... young, thoughtful, systematic ...
• http://www.metamanda.com/marathon/ — Amanda Williams — San Francisco area ... one marathon thus far ... techno & funny ... looking into grad school soon ...
• http://myroadtoboston.blogspot.com — My Road to Boston by Rick Carlsen ...
  

(correlates: PsychologicalUndead, ClassicCorrigendum, TommyBurgerRevenge, ...)