This is an excellent study on CrossFit. The only thing I really dislike about it is that they confounded the results by switching the subjects diets prior to beginning the study. Otherwise, the methods and conclusions seem very solid. Here’s a brief summary (the emphasis is mine):

CrossFit-style training can significantly improve maximal aerobic fitness and body composition even in trainees with above average aerobic fitness. However, there is a risk that this type of training could lead to overuse injury and therefore care should be taken to vary loads and exercises and to monitor any signs of muscle or soft tissue damage carefully.

Also, one thing that was not mentioned but that I think is important to take notice of: The drop in bodyfat for the study was relatively mediocre across the board (7.61 lbs over 10 weeks for the males, or ~0.76 lbs per week) and the gain in muscle was virtually non-existent (around 2lbs over 10 weeks for both groups). So it doesn’t seem to be a highly effective method of either removing bodyfat or increasing muscle mass, especially for the amount of effort expended.

Here’s the full article:

Can CrossFit improve aerobic fitness and body composition?