The Benefits of Hills
I have long been a proponent of incline running on a treadmill as a key component of rehabbing knee injuries while limiting a loss of conditioning. Running on an incline provides very favorable joint kinematics during running gait, signficantly decreasing the amount of load on the hip and knee.
I have recently spent some time looking at articles related to implementing hill running into a general running routine, both as a seperate hill training day as well as adding a shourt course into regular runs. There is very good efficacy behind this to improve our speed and quite possible decrease our risk of injury.
I particularly favor adding a course of hill sprints or short hill reps into a regualr long run to work on efficiency and power.
The linked article, by Jason Fitzgerald of StrenghtRunning provides what I think is a nice overview of some of the ways to use hills in training as well as some solid advice for you to start playing with.