I think dividing things up promotes growth. There will always be some people who are more comfortable with only one or two places to post, but I think people will gravitate to small groups if given an option.

I'd suggest making Protein Power separate from Atkins. As one who's done both, they are different. I'm rereading PPLP right now, and it's more obvious to me than it was the first time I read it how different they are.

Karen's "start a thread and see if it grows" idea is a good one too. Can you do a search on profiles and find out how many people are doing what? I haven't noticed many Zoners (but I may have missed them).

(I also think Schwarzbein is quite different from Sommercising.)

I'd post in a Protein Power forum and read the others for info, for what that's worth