The Black Diamond Games forum seems to be serving its purpose. After less than two weeks, we're up to 59 members, with some good discussion and organization. Pulling the plug on Meetup was a leap of faith, but I think it was the only way to transition over cleanly.
We've got a few features we're investigating. The biggest shortcoming compared to Meetup is the lack of an RSVP function. I'm told we may have that shortly.