Has your Sim ever been invited to another Sim's party - birthday, whatever?

I wouldn't say, that it is often, I am being invited to birthday parties, but it happens every now and then. Just not enough for me to be bothered by it, as I don't actually want the invites (for birthdays that is).

EDIT: You do have to have inactive or unplayed sims that are close to aging up, in order to get the invites. Since all sims are at the start of an age when created, this won't happen unless you have aging on for inactive sims. Or alternately, play them a bit with aging on, or download pre-played sims from the gallery.