Oh boy, the low carb discussion ... it happens every message board no matter what the subject matter. But just remember, most things in life require a fair amount of balence. And cutting essential things from your diet ... like carbs ... is not balence.
Your body makes it's energy primarly from carbs, not protiens, converting protiens for energy takes them away from things they should be used for in your body. The no carb atkins thing obtains it's quick initial weight lose from primarly water weight lose and by tricking your body into thinking it's straving to death so it will use it's 'reserves' for energy.
Combined that with, in many cases, a substaintial increase in fats of all kinds, it doesn't really sound, to me, as a reasonable approach to weight lose. You'll really need to start taking suplements to compliment other vitamins you'll be missing by not eating/drinking things like oranges, etc
As for the carbs in the 'no carbs" soda ... dunno how to answer ... but there is the caffine, which can have effects on dieting. It will act as an apatite supressant, but also may cause your body to store more then it normally would. I don't really know the details on that one. It's my wife who's the nutritian nut, not me