I love how everyone says you have to go out FAST because it is really hard to pass in XC. A few years ago we had a sophomore that should have run around 16:45 LEADING at 300 meters. It OBVIOUSLY wasn't too difficult for 61 runners to pass him over the next 4,700 meters. He ran 17:32. By his senior year he was pacing his races great, was more consistent and ran 16:06 at the state.
The problem I see here is that people are only looking at the handful of runners who have a chance to win the race. Most of your runners are going to be in the "pack". That's why it is important to run your own race and to pace yourself properly. It makes ABSOLUTELY NO DIFFERENCE WHAT YOUR SKILL LEVEL IS, if you go out faster than you should in a race, you are going to run a time SLOWER than if you paced yourself properly. Most of the time running a SLOWER time means you will place LOWER. Just because the winner ran a big positive split in a race where EVERY runner ran a big positive split proves nothing.
What most runners do is concentrate what they can run the first mile in. They should be concentrating on what they can run the LAST mile in. That is far more important.
Another point that hasn't been mentioned is the difference between leading and tucking in behind other runners to save energy. You can successfully do this and only be 3 or 4 seconds behind the leader. That little time can be made up very quickly during the 3rd mile when you are less fatigued than the leader.
As for negative splitting being rare, that is NOT the case in the large division at my state meet. Most years they go through the mile slower than the smaller divisions and finish with much faster times.
One point above that shows an obvious lack of knowledge is considering 400,800,1,500 and above races to be the same.
A POSITIVE split should be run in races 800 or shorter. Negative or even splits should be run in races 1,500 or longer.
Of course in XC with varied terrain, you can't always tell by time if a runner is pacing properly. You have to go by place in the race at different points. If they are losing positions, they went out too fast. It they are holding position, they probably still went out too fast. If they are slowly moving up through the field after the first half mile, then they are pacing correctly.