I've had terrible experiences with the usability of ning. It could always just be a private invite only forum. Email me and lets chat more? Email is in my profile.
Maybe something like a ycombinator/reddit/jig/listry clone? What are the options? I like the design of www.jig.com a lot.
Send Zach and email, as I did, and he can loop us all in on email and we can talk about it there....
startupguild.com uses Yammer, which seems to be decent.