Monthly or Quarterly F2F and/or Conf Calls

In my experience with starting groups, I've found it's most powerful when there is a small group that meets up in person (where possible) or via phone, and builds from there.

I think a strategy of having a ning-like site with a fairly low time commitment and using that as topic fodder for periodic (but regular) meetings could be a good way to go. It's scalable and a bit more nimble...