It's not the layout or the tools, it's the community and the conversation.
Any forum such as Ning is a closed ghetto - an echo chamber.
Twitter is open and public. No-one owns or controls it, and it will constantly surprise and entertain you. If you participate as I suggested, people will talk back to you.
Folks, I need your help. Please say Hi to Kevin on Twitter. Suggest how he can improve his Twitter account and explain why Twitter helps you.