I've heard good things about that couch-to-5K program. About a zillion studies suggest that the overwhelming health benefit is garnered by being able to exercise solidly for about as long as it takes to run a 5K. Marathons are great but they don't help you live longer. 3x a week cardio and being able to run 5K nonstop, absolutely does.

I did a few 5k's and 10k's back in the late 80's; I really liked the 10K distance. Not that I was fast, mind you. I never got under 40 minutes but going out for a 35-45 minute training run was SO good for the inside of my head.

Good on ya!