Ran the USMC Marathon Sunday. 30K runners is way too many, but it was quite a thing to experience. My son did something bad to his foot at mile 7, limped to mile 16 and finally tossed in the towel. I finshed at 4:05, was shooting for 4:00,my Runkeeper was jacked and told me I was going at the right pace, but I was not. (30K runners, support folks, cell service was shot, so I think the GPS wasn't accurate)
I can't blame that, really though - I was smoked at the end and don't think I could have gone much faster.