I read something the other day that makes complete sense to me. Hill running is a great way to get a hard workout in, without a lot of pounding on your body. We all know that. What I didn't think about is that the downhill is actually worse on your body. If you're a new runner, then walk the downhills. If you are an intermediate/advance runner, then you can run the downhills. But what I didn't realize, and I can't remember where I read this (Joe Freil?), is that if you're an intermediate/advanced runner, but you have a history of foot/heel/achilles/calf pain, then walk the downhill.
Good advice. Plus, it's too early in the season to injure yourself!