What a mighty fine question and one I asked myself. So I am not going to go in a lot of detail because I couldn't quite capture the scientific explanation of it quite like Mark and Loren do. So the short version is this; our ancestors ate a diet that mostly contained meat, fruit, vegetables, spices and nuts. No grains (yes, corn and rice are grains) and no dairy (for the Paleo diet only) and no processed sugar (honey and maple syrup is ok in small amounts). The intake of process foods especially grains are bad for you. It messes with your insulin levels. This lifestyle is unlike another low-carb diet and I have had amazing results with it. In a month of mostly just "dieting" I have already lost 9 pounds and I feel amazing. I have a list of links on my home page that include http://www.marksdailyapple.com and http://thepaleodiet.com/ to help you do your own research on just exactly what the Primal/Paleo "diet" is and why it is most beneficial for you.
I am also starting what is called Intermittent Fasting which Mark talks about briefly here: http://www.marksdailyapple.com/fasting I first heard about this from my mom who sent me an article by Mike Geary creator of Truth About Abs, http://www.truthaboutabs.com/. Feel free to do some research and see what you think.
I often blog about recipes I have tried out and enjoyed. I am strictly using Primal and Paleo friendly recipes which I have gotten from some amazing cookbooks:
The Primal Blueprint Cookbook
The Primal Blueprint Quick and Easy Meals
Paleo Comfort Foods
Make It Paleo
The Paleo Diet Cookbook