If you want to have an action happen on user who logs in first time and logs in right after the registration, without email verification. You can use the event "After saving a new user account" problem here is the in conditions you will not have any data about the current logged in user, as he will be logged in after that. So even if you check global $user it looks like the anonymouse user.
So what I used here is $_session['some_var'] and set a flag there, so when the same event happens again when I use Invite OG users and news users are created again, this is not fired. This could be a bit confusing how I explained it, but this is what you do if you want to fire an event only once with user immediately logging in.