I do a 60 second *steep* uphill run at 8.5mph, then jog/walk back down, but not allowing the rest period to go over 3minutes. Repeat this as many times as you can.
It works the calf muscles over a longer range and the downhill will gently improve the dorsi-flexor muscle which is the cause of the burning stiffness on the front-outside high bit of your shin just under the knee, that muscle there. Poor dorsi-flexors will cause shin splints.
It's also good for the heart and will greatly help build stroke volume.
It won't make you any better at running further though, but strength is great. It also releases those lovely running drugs that make you feel like you've had a hard run!
I also use hills when my legs are stamina-tired since there is less shock on them on average and it stops them going into the long-run fatigue state I still seem to suffer
Hills rule!
