Well, there are some in the CrossFit community who are not keen on super long workouts either, like Robb Wolf mentioning issues with workouts longer than 45 minutes increasing cortisol levels and such.

I think a varied approach is a good thing though, because the caveman never know if he would find a bear in his cave, or have to run for an hour to catch a deer.

Here is also a recent blog post by Dr. Harris of PaNu regarding "Body By Science". http://www.paleonu.com/panu-weblog/2010/2/22/body-by-science-and-panu.html

Well, there are some in the CrossFit community who are not keen on super long workouts either, like Robb Wolf mentioning issues with workouts longer than 45 minutes increasing cortisol levels and such.

I think a varied approach is a good thing though, because the caveman never know if he would find a bear in his cave, or have to run for an hour to catch a deer.