Thank heavens this feature has finally arrived.
People are sometimes surprised when I tell them this is _the_ number one most important feature to me. I sometimes need to give my little siblings a ride from/to their workplace -- it's a great thing to be able to use iPhone's 'Find my Friends' to see where they are so I know where to pick them up. Or to see where my significant other is if she's coming from a different city (and when she asks for directions, I can actually be of help because I know where she actually is).
Now, if only iOS and Android had better interoperability... so that I could use my iPhone's 'Find my Friends' app to easily locate my little brother's Android phone.