For those still interested in this subject. Precision Nutrition laid out a brilliant objective review of the Paleo diet itself.
http://www.precisionnutrition.com/paleo-diet
In Summary, don't buy into the evolutionary argument, you would be surprised at how well our body adapts to the modern diet.
However, that doesn't say a modern processed diet is a good thing.
They studied tribes in Africa, South America and even the Arctic who thrive off a diet more paleolithic than any American can dream of. Turns out, they all have their pros and cons, but we do see some health indicators that favor the diet.
You don't
have to entirely ditch grains in favor of veggies. Most evidence that grains are "bad for you" has been extensively debunked.
Thats not to say the Paleo diet is bad. For those with digestive issues, diabetics, celiacs or desiring to lose body fat, Paleo is solid.
It really comes down to a "to each his/her own" method of dialing in their nutrition. The concept is simple and effective, but you don't have to exclude grains like most Paleo proponents seem to badger on.