I think it's interesting what different runners think about while they run. Some focus on themselves: their posture, their footstrike, their pace, their breathing, their muscle condition, their heartrate, or any number of things. Others focus on the scenery, the guys or girls around them, talking with friends, the next water break, work, music, or anything to take their minds off the task at hand.
While I am very un-scientific here, I think the associative runners, the first group described above, are generally the higher performing runners (this is also consistent with the few studies done in this area). The dissociative runners generally are more recreational in nature and not so concerned about performance. Not that there's anything wrong with either!
I definitely fall into the associative group. I'm constantly monitoring my speed (usually through my breathing rate and effort), my distance covered and still to go, my footstrike, and any number of other technical issues. It's amazing the differences in this approach and some of my work associate's approaches.
But, any approach works. I suppose it just depends on your goal. Mine is not to watch the girls and is to focus on the task at hand. It works for me; I'll stay with it.