I read your post as you were some sort of event planner or something, not that you were using it in a personal group of friends. Please forgive the misunderstanding. I see a lot of groups/businesses that use facebook exclusively to communicate and organize events (like the local paintball field) and they are missing out on some people (I have no idea how to quantify how many). I'm sure they're reaching more people now (using facebook) than they were using whatever old method they were using.