I think the number of people who won't use meetup exceeds the people who won't use facebook at this point. I despise facebook but it's a necessary evil. Meetup is just a terribly clunky site I hope I never need to log into ever again. I go to some meetups that happen to be on meetup, but find the times elsewhere, or they're a weekly meetup so I already know the time. They may have dominated the space, but if you use meetup, some will just ignore the meetup group.