We had employer-sponsored coverage in September, when Claire was born. Then we had the same plan, but paid for out-of-pocket with COBRA, in October. Explaining this to the pediatrician's office (so we don't have to pay the bill they sent) took some effort and several phone calls to verify information.
I'd say "at least that's done now", but starting November 1, we have a new employer-sponsored plan. So the next time we go to the pediatrician, I'll still have to make sure I update the insurance info they have on file.