Here's a quote off of Atkins site:

"Excessive caffeine may cause unstable blood sugar and should be avoided by those who suspect they are caffeine dependent. Everyone should try to avoid caffeine. "

What I read from this is it could cause cravings with the unstable blood sugar part. I don't see here that it would cause you to gain, or even stall.

I don't want to give up my coffee. It's my best friend in the morning. I don't use anything but cream, no artificial sweeteners.

I suppose this would be more of a personal choice, but I just don't understand what the negatives are here.