The gym that I belong to just got some incline trainer treadmills that go from -3% to +30% incline. Never tried them yet but think you can probably do some creative hill workouts on them. Anyone use them regularly? I'd probably get some strange looks if I tried doing hill bounding or hill sprints on them but was thinking of doing some slow pace hill reps to work on the calves.
bump
I just got done doing a 6 week block of training at 12% incline or greater. Went on vacation and the first day I ran on the flatland my legs were extremely sore. Took all week before the soreness finally went away.
I think the best use would be if you can run a program where you go uphill, downhill, and level during the run. That way you are using different muscles all the time and may help keep away overuse injuries.
What most people do is try to run too fast a pace when the incline is very steep. After a minute, they decide it is too hard and decrease the incline. Add at least 20 seconds per 1% increase in incline and you should be fairly close.
Regardless of what workouts you come up with, start slowly and work your way to maximum effort over about 4-6 weeks so the muscles you are using don't get overworked.