After reading the post on James Loehr's "toughness training" I realized that I might be overtraining by running 3-4 times a week, and not allowing adequate rest and recovery. The information from Doug McGuff also reinforces that you need to push hard, but then allow enough rest between workouts. So I took a break of 6 days since my last run, and today I went for my first run this week. I really pushed myself, and it was amazing...I shaved 30 seconds off my best 5-mile time. That's quite a big improvement for me, and great, because I'm training for a relay that is just 6 weeks away, and I was not making much progress with my time. What's more, I just seemed to have a lot more energy today, especially towards the end of the run. My strides were longer and more energetic. I think the time off helped me build up some reserves.
I'm thinking of going to 2 runs per week, with some resistance training or cross training thrown in, to mix it up. I definitely see that overtraining is a big risk that people give lip service to, but don't always take seriously.