Its not generally regarded as an activity that will enhance running (great time for cross country skiing as an enhancing activity!!) but is regarded as complementary. Certain running plans such as Firman FIRST incorporate a couple of cycle/spin days as a minimum per week. For me, I use rowing to complement running. Too many miles and I am susceptible to injury, so I see rowing/spinning/swimming etc as great for cardio workouts. However, proof will be in the racing as I haven't ran an event yet under my new regime.
I don't think I'm in 2:10 marathon shape yet though
Edited: 23/01/2013 at 17:14