Funny, I don't count individual carbs, nor am I restricted to less then 20 carbs per day. I am pretty sure Atkins was clear that you progress towards the number of carbs you can handle, based on activity level, etc. He suggested the typical amount for weight maintenance would be around 50 carbs per day, from veggies and complex grains such as oatmeal.

The biggest difference between these diets is that South beach takes longer (it introduces carbs earlier) and South Beach is still sat fat phobic. Most people I know who did South Beach struggles due to the crappy low sat fat food choices leaving taste wanting.

I know several people who simply added sat fat backt to their diet (ala Atkins) and suddenly they lost more weight and were happy on low carb.