I think what people really need to do is identify clearly what there goals are and then look long term. Many triathletes look to and focus on running a marathon as part of their seasonal goals in the hope that it will improve their running both overall and for triathlon. My guess is that it does neither.
It really depends on your background. If you come from a background of years and years of running you are in a different category than someone who got into triathlons and started running at roughly the same time. I ran for 6 years at a high level before I took up triathlons in the early 80's. What I found was that I was able to reduce my total run volume and number of runs/week, but was still able to maintain run performance. However, I had been running 6 -7 days/week for six years. If you just started running when you started triathlon training, then I think the best approach is to do a 4 - 6 month running focus, doing just enough swimming and cycling to maintain a bare minimum fitness level. Your running will really go up and I think that many would be surprised how quickly the swimming and cycling would bounce back once they returned to a more balanced program.
Fleck
Steve Fleck @stevefleck | Blog