Here's a slightly different perspective.
One of the reasons that I like to train is because it makes me better equipped to deal with the challenges of my daily life. whether that means getting a twenty-pound tub of something off of a high shelf, moving a friend's couch up the stairs, pushing someone's car out of a ditch, or whatever it is.
Doing LSD (Long Slow Distance--what did you think I was talking about?) cardio doesn't really help that much. How often do I have to get up and run six miles? If I'm in the army, sure, it makes sense. But I'm not. It's much more likely that I'm going to have to sprint to catch a bus or carry kegs up a flight of stairs or help someone move. Activities that are aerobic, but not in the way running is.
Here's another experiment to try. Swim laps for distance, then run for six weeks. No weight training, no swimming. Now swim again. Could you go any faster or farther? No. So how is this useful, all-around training?
Try the same thing with a well-designed weight training program--no running, no swimming--and I bet you'll be able to swim farther. The point is that running isn't specific to very much except running, whereas strength is a prerequisite to everything, including running.
So yeah, I'll do some GPP work and HIIT. But LSD? Not any more.
Dan "Kettlebells" McVicker