I have found the same thing to be true as Grog said.

When I trained for the marathon, I read an article in Runners World that encouraged run/walking long distances. Part of the point was to give yourself a little breaks throughout the run so you wouldn't completely cache out your legs.

I gave it a try. I knew there would be breaks every mile at Chicago which I planned to utilize. So every 10 minutes on my long weekend runs, I walked for 20-45 seconds. You don't want to walk for too long, because your legs will start to cramp.

I found I had negative splits when I did a couple half-marathons in training. And I ended up having a good marathon for me. I was by far less sore the next day than DH who pretty much ran the entire marathon without walking at all.

Here's an article on walk/running:
http://www.jeffgalloway.com/training/walk_breaks.html