We bought a 7 day pass for green cars. Went to make reservations 3 days in advance and was unable to make a reservation in green car, almost didn't get one in regular car. Made another reservation a week out and couldn't get the time we wanted. If you're primarily using it for the Shinkensen trains, There's limitations.Most trains bullet trains available for JR pass only run once per hour, while Nozomi trains run much more frequently and have direct routes without transfers.
We asked the guy at the train office why the trains were so busy on a Wed. and he said these are trains for JR pass holders. So if you buy one these make your reservation as early as possible.
We thought we would save a few bucks with the pass but are losing money on it because we couldn't get in the green car.