The last group I was in (which will hit 3 years in Sept) did have themes (but that was what worked for us). At the beginning, we started off with the 2nd Saturday of the month so you just knew that's when it would be and could clear your calendar in advance. As it started clicking & becoming important to people we were free to revise. We hosted on a rotating basis and the date became what worked best for (1) the host and (2) the majority of everyone else. We had dinners with anywhere from 2 to 10 people, depending on schedules but I don't think you can expect to get everyone all the time. Good luck!
The role of a librarian is to make sense of the world of information. If that's not a qualification for superhero-dom, what is?
--Nancy Pearl, Director, Washington Center for the Book