Having said that, I'll never leave Facebook until something else replaces it. It's the only place I have to keep in touch with a couple hundred people I would otherwise have no contact with. And it's still common for various groups of people I know to use it for event planning.
I also find myself having to share invites and news with people I know who are not on Facebook. They appreciate it, but I consider it a pain in the ass that they could easily resolve by getting a Facebook account again and just checking it once a week.