When I add a new user, it would be great to know when they've signed in for the first time. That way I'll know when everyone's ready to go and I don't have to keep asking, "Did you sign in yet?"
Two possible ways to get notified:
  1. An email to me saying a new user has signed in for the first time.
  2. An icon next to their name in the People section indicating whether or not they've signed in for the first time.