As to the comm, I like the idea, but I think you'd want to limit membership to people you know well enough (to limit that is possible with the virtual world) to trust. Most of us are respectful when it comes to each others ideas, but I there are some authors who I count as friends with whom I wouldn't share an idea without expecting them to copy/steal it. It's usually pretty obvious pretty quick who can and cannot be trusted in that area.

I do think it helps both in the process of writing and in maintaining interest projects to be able to talk about them.