I recognize that the best source of nutrients is ultimately from GOOD food. However, I do have concerns that the majority of the food may have its issues. (Pesticides, Hormones, Antibiotics, Irradiated, etc) Without opening that can of worms, I personally choose to take a high potency multivitamin to cover my nutritional insurance.
As crossfitters, we demand a lot from our bodies. Crossfit workouts create their share of free radicals just like any stressful activty. I choose to take some extra Vitamin C (buffered) to help combat this. I also include a protein supplement.
As to the efficacy of supplements, they are not all for naught. Unfortunately, some of studies have been flawed and have questionable funding sources.
I think Crossfit is great promoting the Zone Diet. At least it gets the group making healthier choices.