i have heard people say that aspartame has caused a stall in weight loss, and I know there are some heath concrens about it's uses. I guess that is a personal decison.

Atkins says that he has seen aspartame cause people to stall, I have not experienced it, I drink a ton of soda (a lot of water too.)
My concern would be more with the caffene, I love the energy boost; but, it does in some people (including me) increase appetite. Willpower will beat hunger, but why make the mountian higher?