Uhm, why mention Facebook if you don't list three features that are unique to Facebook or were pioneered by them? Seriously, invites, notifications and comments are hardly new concepts. They're good concepts, but they have nothing to do with Facebook.

If you want to mention something that was pioneered by Facebook and that you should copy, then it's the use of real names instead of usernames or handles. This feature is what allowed people to connect with each other over Facebook when having no other communication channel, i.e. reconnecting with old friends or classmates.