Same here. I'm on Facebook because of events.
Years ago, a club I was in was using Yahoo Groups, and over time more and more events were posted to Facebook. People complained, and eventually the organizer wrote back "I've been using Facebook because it lets me schedule an event, track RVSP's, link to the location/map, add members, post pics, and help advertise/recruit for more members. Anybody that wants to help or takeover any or all of this, let me know".
Total silence for a day or two before about 50 of us joined Facebook.
That was 8 years ago. I moved away but now I'm in at least 4 clubs that actively use Facebook for events... now it's typical for friends to schedule birthday parties, housewarmings, plain old get-togethers via Facebook private events. Also alumni groups, community events and so on that keep in touch or advertise things to do that way.
The only thing I'm tired of is people that constantly mention how they quit Facebook. I don't care. It serves a useful purpose for me. It's like that Onion article about the guy who doesn't own a TV and mentions that as often as possible - Onion should do an update starring Facebook quitters.
And before anybody suggests it, Meetup isn't a good alternative. (I'm an organizer of a Meetup group as well; I like Meetup but fills a different niche.)