I still have some of it in my house, but over the past year I've cut down majorly, by refusing to snack during the day, and tracking my calories each day. Just being aware of what I ate made a huge difference. Also, instead of ice cream, I buy TruFru dark chocolate raspberries and just have a few each night. I've lost about 50 pounds since last January through diet and exercise.
I'd say it's more like 70/30 personally. It also gives you some wiggle room with a low cal diet. But you definitely can't just do some running then go out for bucket of KFC all the time.
Calories burned from running isn't that great of a return.
An estimate is that a 200 pound person burns 792 calories per hour running at 5mph (12min/mile, or 8kph) on a firm, level surface. A 140 pound person burns 555 calories in the same scenario.
So yeah, with a 1500 calorie deficit diet, that's about a 3rd of what you eat for the day, so like 33%. That's a pretty big chunk, and easily allows you to snack on occasion and still hit your deficit. I'd say it's pretty helpful, but diet is still absolutely necessary for any results.