I've also only hear that incline training is great for working your backside. I don't think you would bulk up.
BUT - I was listening to a running podcast a couple of weeks ago (The running shoe) and the guy recommends not running at an incline for longer than a few minutes, and make sure you are running fast enough that your can stay on your forefoot rather than trying to land on the heel. He said that incline running for long periods can damage you achilles tendon by overstretching it.