I like this graphic of marathon split times:
http://twitpic.com/1hkwqw
It reminded me of the marathon I ran pacing Fritz. Fritz's goal was 8 minute miles for a 3:30 marathon. He took off and ran 6:50 for the first mile. He said he felt good. I talked him in to easing off the pace. I think we ran a few 7:10-7:30 miles. Every split I'd suggested easing off a bit. My plan was to run to the half point and then stop, but I felt quite good and decided to run the entire distance with Fritz. In the second half we gradually slowed down. I felt fine, but didn't want to abandon Fritz (since my job was to be the pacer). At some point beyond the 20 mile mark, Fritz went from running around a 8:50 mile to something like 11:30. It happend in a stretch of maybe 50 meters. I found it interesting that Fritz didn't sense that he'd slowed at all. We shuffled in the last few miles and finished in 3:23. So, met the goal with time to spare, but it sure wasn't an easy way to run 3:23.